Fresnel Lens Solar grill - fresnel solar lens

 2024-11-18 06:34:49

Laser pointer green laserprice

The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

So how safe are these things (the sub-5mW class IIIa version)? They won't burn you. They won't cause permanent eye damage. Tests were performed on individuals who were scheduled to have an eye removed for medical reasons. For the purposes of the test, the eye was normally functioning. Test subjects stared directly at 5 mW lasers with there to-be-removed eye for five to fifteen minutes from various angles. No permanent eye damage occured. Some changes in tissue were noticed. Of course, in a real-world incident, laser light entering the eye would likely last for less than one second, as people naturally look away from bright things and close their eyes, so there is no real danger of direct damage. Having said that, these things are damn bright. If you hit a car driver at night with this, he'd be effectively blinded for at least a few seconds afterwards -- long enough to crash and die and have you go to prison for manslaughter. These are not toys for children. They should never be shined at people ever, and most especially not cars or planes. Finally, why green? Our eyes are most sensitive to green light. The same measured power output of a red laser would not produce a visible beam, because our eyes aren't as sensitive to red. By the time we could see a red laser, it would probably be reaching a dangerous level of intensity. BTG-6-plus Z-bolt offers several green laster pointers in the IIIa class. Note that these are often referred to as 5mW lasers, but they always have to be less. From everything I've read, there is a lot of variation in how much under 5mW the lasers are. I'm not sure how much to believe, but some claim that you can end up with as little as 1.5 mW from some of these products. For this reason, I chose the BTG-6-plus, because this particular product is guaranteed to be tested by Beam-of-Light to be between 4.5 and 5mW limit. Mine actually came with a hand-written sticker on it that said 4.92 mW. It also came in a very nice wooden box, and a pair of batteries. For my order, they were also giving away a free red laser pointer with it. I don't much care about this, but the free red laser pointer was packed into a second plastic foam case, which was much too big for the red laser pointer, but perfect for the green one. I don't know if they always give out this second case for the green pointer, but if you buy a pointer from them I suggest you ask them about it. The wooden box is very nice, but not very practical. The plastic foam case on the other hand is much more practical for slipping into your pocket or some luggage, and it provides nice protection. It closes with a flap that has two snaps in it, and it has slots for a spare pair of batteries. This is the case I'll be using whenever I'm carrying this pointer. So, how does my laser work? It works GREAT! Exactly as described - a green beam of light protrudes up and more or less stops right on the object you are pointing to. The end of the beam is a bit more blurry, and fades slightly, but it really seems to have an end where the beam essentially stops. It's extremly apparent what you are pointing to. I haven't yet tested to see how far away from me it remains visible, although people standing six feet away from me have been able to see it without a problem. What about light pollution? Many web sites say that in light-polluted conditions you won't see the beam, and you'll need more power. I suppose it depends on what they mean. The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see. I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

The next higher class, IIIb ranges from 5 to 500 mW. You can also legally purchase this class of laser in the United States. But there are restrictions on it's use, because these lasers are capable of permanently damaging vision. You can't use it in an environment where the beam could escape to the outside. To be explicit here, this means you can't legally use them outside. Now you may want to adopt a "no blood, no foul" attitude, and that's fine for you. But just know that if you ever make a mistake, or run into a narrow-minded individual, you don't have a legal leg to stand on - prepare for a good screwing. Furthermore, based on my own <5mW product, there is no reason outside of inferiority complex to get a higher power product for astronomical use. So how safe are these things (the sub-5mW class IIIa version)? They won't burn you. They won't cause permanent eye damage. Tests were performed on individuals who were scheduled to have an eye removed for medical reasons. For the purposes of the test, the eye was normally functioning. Test subjects stared directly at 5 mW lasers with there to-be-removed eye for five to fifteen minutes from various angles. No permanent eye damage occured. Some changes in tissue were noticed. Of course, in a real-world incident, laser light entering the eye would likely last for less than one second, as people naturally look away from bright things and close their eyes, so there is no real danger of direct damage. Having said that, these things are damn bright. If you hit a car driver at night with this, he'd be effectively blinded for at least a few seconds afterwards -- long enough to crash and die and have you go to prison for manslaughter. These are not toys for children. They should never be shined at people ever, and most especially not cars or planes. Finally, why green? Our eyes are most sensitive to green light. The same measured power output of a red laser would not produce a visible beam, because our eyes aren't as sensitive to red. By the time we could see a red laser, it would probably be reaching a dangerous level of intensity. BTG-6-plus Z-bolt offers several green laster pointers in the IIIa class. Note that these are often referred to as 5mW lasers, but they always have to be less. From everything I've read, there is a lot of variation in how much under 5mW the lasers are. I'm not sure how much to believe, but some claim that you can end up with as little as 1.5 mW from some of these products. For this reason, I chose the BTG-6-plus, because this particular product is guaranteed to be tested by Beam-of-Light to be between 4.5 and 5mW limit. Mine actually came with a hand-written sticker on it that said 4.92 mW. It also came in a very nice wooden box, and a pair of batteries. For my order, they were also giving away a free red laser pointer with it. I don't much care about this, but the free red laser pointer was packed into a second plastic foam case, which was much too big for the red laser pointer, but perfect for the green one. I don't know if they always give out this second case for the green pointer, but if you buy a pointer from them I suggest you ask them about it. The wooden box is very nice, but not very practical. The plastic foam case on the other hand is much more practical for slipping into your pocket or some luggage, and it provides nice protection. It closes with a flap that has two snaps in it, and it has slots for a spare pair of batteries. This is the case I'll be using whenever I'm carrying this pointer. So, how does my laser work? It works GREAT! Exactly as described - a green beam of light protrudes up and more or less stops right on the object you are pointing to. The end of the beam is a bit more blurry, and fades slightly, but it really seems to have an end where the beam essentially stops. It's extremly apparent what you are pointing to. I haven't yet tested to see how far away from me it remains visible, although people standing six feet away from me have been able to see it without a problem. What about light pollution? Many web sites say that in light-polluted conditions you won't see the beam, and you'll need more power. I suppose it depends on what they mean. The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see. I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

Fresnel Lenses (for Rear Projection TV) Updated 11/5/05 This is an explanation of the fresnel (pronounced "fur-nell" or "frenell") lens panel in a rear projection TV. Return to video topics. Go to other topics. In a Nutshell The screen of a rear projection TV set (RPTV) has two or three layers. The panel with a concentic circular panel, seen only if you look inside, is the fresnel lens. It redirects the light rays to all be parallel, directly out from the screen. If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Green laser pointerAmazon

The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Green Laser Pointernear me

Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

In a Nutshell The screen of a rear projection TV set (RPTV) has two or three layers. The panel with a concentic circular panel, seen only if you look inside, is the fresnel lens. It redirects the light rays to all be parallel, directly out from the screen. If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Laser pointer green laseramazon

Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

So, how does my laser work? It works GREAT! Exactly as described - a green beam of light protrudes up and more or less stops right on the object you are pointing to. The end of the beam is a bit more blurry, and fades slightly, but it really seems to have an end where the beam essentially stops. It's extremly apparent what you are pointing to. I haven't yet tested to see how far away from me it remains visible, although people standing six feet away from me have been able to see it without a problem. What about light pollution? Many web sites say that in light-polluted conditions you won't see the beam, and you'll need more power. I suppose it depends on what they mean. The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see. I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

Bestgreen laser pointer

These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

The screen of a rear projection TV set (RPTV) has two or three layers. The panel with a concentic circular panel, seen only if you look inside, is the fresnel lens. It redirects the light rays to all be parallel, directly out from the screen. If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Green laser background There is a class of lasers, IIIa, which by law must be less than 5mW (of measured optical output, not electrical input). This class is legal to sell in the United States, and legal to operate outside in the United States (local or state exceptions may exist) provided you don't do anything stupid. Shining the laser at aircraft in flight, or moving cars, or other equally moronic acts can easily land you in prison for an extended time (and rightly so). Apparently a man who wanted to see if he could hit airplanes as they were landing was in fact successful. Thankfully, none of the pilots crashed, but the man was reported to have received a seven year prison sentence. The next higher class, IIIb ranges from 5 to 500 mW. You can also legally purchase this class of laser in the United States. But there are restrictions on it's use, because these lasers are capable of permanently damaging vision. You can't use it in an environment where the beam could escape to the outside. To be explicit here, this means you can't legally use them outside. Now you may want to adopt a "no blood, no foul" attitude, and that's fine for you. But just know that if you ever make a mistake, or run into a narrow-minded individual, you don't have a legal leg to stand on - prepare for a good screwing. Furthermore, based on my own <5mW product, there is no reason outside of inferiority complex to get a higher power product for astronomical use. So how safe are these things (the sub-5mW class IIIa version)? They won't burn you. They won't cause permanent eye damage. Tests were performed on individuals who were scheduled to have an eye removed for medical reasons. For the purposes of the test, the eye was normally functioning. Test subjects stared directly at 5 mW lasers with there to-be-removed eye for five to fifteen minutes from various angles. No permanent eye damage occured. Some changes in tissue were noticed. Of course, in a real-world incident, laser light entering the eye would likely last for less than one second, as people naturally look away from bright things and close their eyes, so there is no real danger of direct damage. Having said that, these things are damn bright. If you hit a car driver at night with this, he'd be effectively blinded for at least a few seconds afterwards -- long enough to crash and die and have you go to prison for manslaughter. These are not toys for children. They should never be shined at people ever, and most especially not cars or planes. Finally, why green? Our eyes are most sensitive to green light. The same measured power output of a red laser would not produce a visible beam, because our eyes aren't as sensitive to red. By the time we could see a red laser, it would probably be reaching a dangerous level of intensity. BTG-6-plus Z-bolt offers several green laster pointers in the IIIa class. Note that these are often referred to as 5mW lasers, but they always have to be less. From everything I've read, there is a lot of variation in how much under 5mW the lasers are. I'm not sure how much to believe, but some claim that you can end up with as little as 1.5 mW from some of these products. For this reason, I chose the BTG-6-plus, because this particular product is guaranteed to be tested by Beam-of-Light to be between 4.5 and 5mW limit. Mine actually came with a hand-written sticker on it that said 4.92 mW. It also came in a very nice wooden box, and a pair of batteries. For my order, they were also giving away a free red laser pointer with it. I don't much care about this, but the free red laser pointer was packed into a second plastic foam case, which was much too big for the red laser pointer, but perfect for the green one. I don't know if they always give out this second case for the green pointer, but if you buy a pointer from them I suggest you ask them about it. The wooden box is very nice, but not very practical. The plastic foam case on the other hand is much more practical for slipping into your pocket or some luggage, and it provides nice protection. It closes with a flap that has two snaps in it, and it has slots for a spare pair of batteries. This is the case I'll be using whenever I'm carrying this pointer. So, how does my laser work? It works GREAT! Exactly as described - a green beam of light protrudes up and more or less stops right on the object you are pointing to. The end of the beam is a bit more blurry, and fades slightly, but it really seems to have an end where the beam essentially stops. It's extremly apparent what you are pointing to. I haven't yet tested to see how far away from me it remains visible, although people standing six feet away from me have been able to see it without a problem. What about light pollution? Many web sites say that in light-polluted conditions you won't see the beam, and you'll need more power. I suppose it depends on what they mean. The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see. I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

Having said that, these things are damn bright. If you hit a car driver at night with this, he'd be effectively blinded for at least a few seconds afterwards -- long enough to crash and die and have you go to prison for manslaughter. These are not toys for children. They should never be shined at people ever, and most especially not cars or planes. Finally, why green? Our eyes are most sensitive to green light. The same measured power output of a red laser would not produce a visible beam, because our eyes aren't as sensitive to red. By the time we could see a red laser, it would probably be reaching a dangerous level of intensity. BTG-6-plus Z-bolt offers several green laster pointers in the IIIa class. Note that these are often referred to as 5mW lasers, but they always have to be less. From everything I've read, there is a lot of variation in how much under 5mW the lasers are. I'm not sure how much to believe, but some claim that you can end up with as little as 1.5 mW from some of these products. For this reason, I chose the BTG-6-plus, because this particular product is guaranteed to be tested by Beam-of-Light to be between 4.5 and 5mW limit. Mine actually came with a hand-written sticker on it that said 4.92 mW. It also came in a very nice wooden box, and a pair of batteries. For my order, they were also giving away a free red laser pointer with it. I don't much care about this, but the free red laser pointer was packed into a second plastic foam case, which was much too big for the red laser pointer, but perfect for the green one. I don't know if they always give out this second case for the green pointer, but if you buy a pointer from them I suggest you ask them about it. The wooden box is very nice, but not very practical. The plastic foam case on the other hand is much more practical for slipping into your pocket or some luggage, and it provides nice protection. It closes with a flap that has two snaps in it, and it has slots for a spare pair of batteries. This is the case I'll be using whenever I'm carrying this pointer. So, how does my laser work? It works GREAT! Exactly as described - a green beam of light protrudes up and more or less stops right on the object you are pointing to. The end of the beam is a bit more blurry, and fades slightly, but it really seems to have an end where the beam essentially stops. It's extremly apparent what you are pointing to. I haven't yet tested to see how far away from me it remains visible, although people standing six feet away from me have been able to see it without a problem. What about light pollution? Many web sites say that in light-polluted conditions you won't see the beam, and you'll need more power. I suppose it depends on what they mean. The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see. I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Return to video topics. Go to other topics. In a Nutshell The screen of a rear projection TV set (RPTV) has two or three layers. The panel with a concentic circular panel, seen only if you look inside, is the fresnel lens. It redirects the light rays to all be parallel, directly out from the screen. If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Go to other topics. In a Nutshell The screen of a rear projection TV set (RPTV) has two or three layers. The panel with a concentic circular panel, seen only if you look inside, is the fresnel lens. It redirects the light rays to all be parallel, directly out from the screen. If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Updated 11/5/05 This is an explanation of the fresnel (pronounced "fur-nell" or "frenell") lens panel in a rear projection TV. Return to video topics. Go to other topics. In a Nutshell The screen of a rear projection TV set (RPTV) has two or three layers. The panel with a concentic circular panel, seen only if you look inside, is the fresnel lens. It redirects the light rays to all be parallel, directly out from the screen. If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

Green Laser pointer10000mw

Laser pointer green laserfor sale

It also came in a very nice wooden box, and a pair of batteries. For my order, they were also giving away a free red laser pointer with it. I don't much care about this, but the free red laser pointer was packed into a second plastic foam case, which was much too big for the red laser pointer, but perfect for the green one. I don't know if they always give out this second case for the green pointer, but if you buy a pointer from them I suggest you ask them about it. The wooden box is very nice, but not very practical. The plastic foam case on the other hand is much more practical for slipping into your pocket or some luggage, and it provides nice protection. It closes with a flap that has two snaps in it, and it has slots for a spare pair of batteries. This is the case I'll be using whenever I'm carrying this pointer. So, how does my laser work? It works GREAT! Exactly as described - a green beam of light protrudes up and more or less stops right on the object you are pointing to. The end of the beam is a bit more blurry, and fades slightly, but it really seems to have an end where the beam essentially stops. It's extremly apparent what you are pointing to. I haven't yet tested to see how far away from me it remains visible, although people standing six feet away from me have been able to see it without a problem. What about light pollution? Many web sites say that in light-polluted conditions you won't see the beam, and you'll need more power. I suppose it depends on what they mean. The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see. I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

Finally, why green? Our eyes are most sensitive to green light. The same measured power output of a red laser would not produce a visible beam, because our eyes aren't as sensitive to red. By the time we could see a red laser, it would probably be reaching a dangerous level of intensity. BTG-6-plus Z-bolt offers several green laster pointers in the IIIa class. Note that these are often referred to as 5mW lasers, but they always have to be less. From everything I've read, there is a lot of variation in how much under 5mW the lasers are. I'm not sure how much to believe, but some claim that you can end up with as little as 1.5 mW from some of these products. For this reason, I chose the BTG-6-plus, because this particular product is guaranteed to be tested by Beam-of-Light to be between 4.5 and 5mW limit. Mine actually came with a hand-written sticker on it that said 4.92 mW. It also came in a very nice wooden box, and a pair of batteries. For my order, they were also giving away a free red laser pointer with it. I don't much care about this, but the free red laser pointer was packed into a second plastic foam case, which was much too big for the red laser pointer, but perfect for the green one. I don't know if they always give out this second case for the green pointer, but if you buy a pointer from them I suggest you ask them about it. The wooden box is very nice, but not very practical. The plastic foam case on the other hand is much more practical for slipping into your pocket or some luggage, and it provides nice protection. It closes with a flap that has two snaps in it, and it has slots for a spare pair of batteries. This is the case I'll be using whenever I'm carrying this pointer. So, how does my laser work? It works GREAT! Exactly as described - a green beam of light protrudes up and more or less stops right on the object you are pointing to. The end of the beam is a bit more blurry, and fades slightly, but it really seems to have an end where the beam essentially stops. It's extremly apparent what you are pointing to. I haven't yet tested to see how far away from me it remains visible, although people standing six feet away from me have been able to see it without a problem. What about light pollution? Many web sites say that in light-polluted conditions you won't see the beam, and you'll need more power. I suppose it depends on what they mean. The first time I used it, I was in a rural area, although not very far from the city, and there was a setting gibbous moon. Limiting magnitude was around 5.0, maybe 5.5. The laser was bright and easy to see. I've also used it in Cambridge Massachusetts, easily one of the most light-polluted cities on this planet. On the best moonless nights, limiting magnitude is 4.0. Again, the laser is easily visible, not quite bright, but not dim either. However, this only accounts for the light pollution - I was on a dark rooftop on a slight hill above other lights. So the light pollution was in place, but I had no lights in my eyes. If, by light pollution, you mean standing on a brightly lit street with a street light above you, then no, you won't see the beam. But if you mean, can you see it from a dark spot in the worst light-polluted sky imaginable? Yes, you can see it. Just for perspective, I used it about 45 minutes after sunset. The sky was still quite bright, with 20 minutes of nautical twilight left, and an hour of astronomical twilight. Limiting magnitude was perhaps 3.5. The beam was visible in these conditions. Dim, but unmistakably visible. These lasers are also supposed to work poorly in cold weather. I've used it in below-freezing temperatures. I was carefully to keep it in an inside pocket, or up my sleeve, when I wasn't using it. It worked fine. It tends to come on at less than full brightness, and then brighten up after a fraction of a second. Magic? So why DOES that beam of light simply stop at the target, instead of fading out in the distance, or seeming to go on "forever". Well, the answer's obvious if you do the math. If the laser is one foot away from my eyes, to the side, and I'm looking towards the "end" of the beam, then we can start to think in triangles, where the base is 1 foot long. If I look at a point 100 feet along the beam, then we have a tall skinny triangle with sides of 1 foot, 100 feet, The small angle for this triangle is 0.57 degrees. That's the angle between my sight line and the laser beam. But that means that the other angle is 89.42 degrees. The first 100 feet of beam covers 89.42 degrees of view to my eye. Let's look a thousand feet down the beam. We now cover 89.94 degrees of our field of view. Going ten times farther filled an additional 0.37 degrees of our field of view with a beam. At 10,000 feet, we get to 89.99 degrees - and we gained 0.05 degrees or three arcminutes. Beam-of-light technologies claims their beam from this product reaches 25,000 feet. If that's the case, then the additional 15,000 feet past what we just calculated will add 0.003 degrees to our view of the beam, or 10 arcSECONDS. The first 10,000 feet gives us a laser beam across almost 90 degrees of our view. And the next 15,000 feet of beam visually lengthens the visible beam by a size smaller than the disk of Saturn, Jupiter, or Venus. In other words, while the beam is fading out gradually, the part of it that we can actually see, the close part goes almost all the way to where we're pointing, while the long long section that fades out, adds almost no visible length to the beam. Even the section of the beam starting after one thousand feet away only lengthens the visible beam by the size of a crater on the moon that's too small to see with the naked eye. Where to buy? There are tons of people out there selling green lasers, and lots of horror stories. I chose Beam of Light Technologies because they've been in business for more than five years - I know this because I found a couple of negative reviews of them online from that long ago. But I found no recent bad reviews, and they were still in business. I'm perfectly satisfied with the product and with their service, although one could argue that when everything goes well, you haven't really tested their service. I apologize for writing in this space that Howie Glatter never answered my email. Apparently, spamassassin ate the email, and I found it later. By that time I'd already purchased my product. He has a good reputation, seems a bit pricy, but otherwise I can't comment on the quality of his products or services. Fine's Home Send Me Email

Bestlaser pointer green laser

Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

This is an explanation of the fresnel (pronounced "fur-nell" or "frenell") lens panel in a rear projection TV. Return to video topics. Go to other topics. In a Nutshell The screen of a rear projection TV set (RPTV) has two or three layers. The panel with a concentic circular panel, seen only if you look inside, is the fresnel lens. It redirects the light rays to all be parallel, directly out from the screen. If you ever dismantle the screen of an RPTV, you must be sure to re-install the fresnel lens with the ridged surface facing forwards. Also the fresnel lens must be behind the lenticular lens (ribbed) panel or frosted (diffusion) panel. Just before reaching the screen, the light rays from the projection unit down below are ever spreading out (diverging). The purpose of the fresnel lens is to aim, or redirect, all of the light rays to be parallel, directly out of the TV set. An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

An ordinary convex lens will do this job. But it must be as large as the screen and it would be thick, heavy, and expensive. A fresnel lens has the same curvatures as an ordinary lens, redirects (refracts) the light the same way, but is collapsed down. For the RPTV, the fresnel lens has thousands of ridges in a circular pattern and is a panel about one eighth to one quarter of an inch thick overall. An ordinary lens can have the curved surface facing either way, requiring only minor calibration differences for focusing. A fresnel lens must be positioned so the ridged surface is on the side of the parallel rays, which means outwards for an RPTV. Note that on the fresnel lens, some of the surfaces of the ridged side are perpendicular to the flat surface and the other surfaces are not. The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.

The light rays will miss the perpendicular surfaces when the flat side is facing inwards, towards the projection units. This ensures that all of the light rays come out parallel. With the fresnel lens reversed, light rays will hit the perpendicular surfaces. (An ordinary lens does not have these perpendicular surfaces.) When this happens the rays will go off in many different directions (scatter). The rays don't have to go far (just another 1/8 to 1/4 inch) before reaching the front screen surface but you will see excessive haloing. The lenticular lens is also a panel 1/8 to 1/4 inches thick. It takes some light rays from each spot on the screen and redirects them to each side while directing less light upwards and downwards. This gives a more even brightness for viewers sitting off to the sides. The diffusion panel (a frosted panel optionally used instead of the lenticular lens) does not have the graininess caused by the rib spacing of a lenticular lens. It allows more light to travel upwards and downwards necessitating more brightness from the projection unit to give the viewers an equivalent picture. Fresnel lenses come in different shapes for different purposes. Some are equivalent to concave lenses as opposed to convex lenses. Click here for more information: http://www.3dlens.com Go to our video hints page Go to table of contents Contact us All parts (c) copyright 2000, Allan W. Jayne, Jr. unless otherwise noted or other origin stated. If you would like to contribute an idea for our web page, please send us an e-mail. Sorry, but due to the volume of e-mail we cannot reply personally to all inquiries.