Dichroic optical filters consist of thin film dielectric coatings on glass and exhibit sharp transitions between transmitted and reflected wavelengths. Dichroic filters are similar to traditional interference filters but differentiate themselves by reflecting all unwanted wavelengths. Consequently our dichroic range also offers minimal absorbance characteristics.

Linea uses Teledyne DALSA's own advanced CMOS line scan sensors with high QE and low noise for better image quality. Available in resolutions from 2k ...

dichroicmirror中文

Our dichroic filters are available in longpass, shortpass, bandpass, bandblocking and colour correction types over a range of wavelengths. Dichroic shortpass and longpass filters can also act as hot and cold mirrors respectively.

To answer your question, Yes, you can change lenses in mid roll. Most film slr cameras are designed to be able to do that. That is one of the things that makes ...

Housing for Optical Fiber Collimator. Using this housing with collimator lens (FCL), the output beam from FC connector fiber is collimated.

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

dichroic中文

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

Laser Shaft Alignment Systems for Easy alignment of couplings. We provide systems from SKF, Domilini, Easy Laser, Monarch and more.

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

Dichroicmirror

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

Feb 6, 2005 — "Steel exhibits different colors depending on temperature. Temperatures above 800F produce incandescent colors; the atoms in the steel are so ...

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

Dichroic Shortpass Filters Cut-Off Wavelength Transmission Wavelength Reflection Wavelength Wavelength Range(nm) Wavefront Tolerance Material Diameter 400 325-385 420-485 325-485 1/4λ Fused Silica 12.5 25 450 325-430 470-545 325-545 1/4λ Fused Silica 12.5 25 500 325-480 520-610 325-610 1/4λ Fused Silica 12.5 25 550 400-530 575-725 400-725 1/4λ Fused Silica 12.5 25 600 400-580 625-795 400-795 1/4λ Fused Silica 12.5 25 650 400-630 675-850 400-850 1/4λ Fused Silica 12.5 25 700 400-680 725-990 400-990 1/4λ Fused Silica 12.5 25 750 400-725 800-990 400-990 1/4λ Fused Silica 12.5 25 800 400-775 850-1050 400-1050 1/4λ Fused Silica 12.5 25 850 880-1600 635-805 635-1600 1/4λ Fused Silica 12.5 25 900 400-820 910-1110 400-1110 1/4λ Fused Silica 12.5 25

Low passfilter

When white light is passed through a glass prism it splits into its spectrum of colours (in order violet, indigo, blue, green, yellow, orange and red) and this ...

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

Bandpassfilter

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

Simply speaking, when this disc size exceeds the size of a pixel in your cameras sensor then you will have diffraction or your camera is then regarded as being ...

Dielectric mirror

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

"Can't say enough good things about this UV cure light and the seller. The light is high quality and perfect to cure resin in tight spaces. The seller: awesome.

Hyperion Optics’s complete range of cost effective dichroic filter range offers superior transmission, reflection and absorption characteristics.

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

Notchfilter

201618 — Chromatic aberration in spherical lenses. Chromatic aberration occurs because the lens refracts the various colors present in white light at ...

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

Apr 22, 2011 — A telephoto lens is optimized for long reach (good magnification at long distances). A zoom lens is one with variable focal length, usually ...

Opticalfilter

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

Hyperion Optics’s complete range of cost effective dichroic filter range offers superior transmission, reflection and absorption characteristics. Key Features: Sharp transition from reflection to transmission High transmission in pass band Hard coatings and no adhesives for long filter life span All dielectric coated with IBS technology Factory Standard – Contact us for manufacturing limit or custom specifications Angle of Incidence: 45.0° Shortpass Type Transmittance: Tabs>85% Dimensions: 25.2mm*35.6mm*1.1 mm Clear Aperture: >95% Operating Temperature: -45°C ~ 85°C Physical Durability: MIL-C-48497A Longpass Type Transmittance: Tabs>90% Reflection Band: Rabs>98% Thickness Tolerance: ±0.1 mm Transmitted Wavefront: 1/4λRMS@633nm (per inch) Environmental Durability: MIL-STD-810F Substrate: UV Grade Fused Silica Dichroic optical filters consist of thin film dielectric coatings on glass and exhibit sharp transitions between transmitted and reflected wavelengths. Dichroic filters are similar to traditional interference filters but differentiate themselves by reflecting all unwanted wavelengths. Consequently our dichroic range also offers minimal absorbance characteristics. Our dichroic filters are available in longpass, shortpass, bandpass, bandblocking and colour correction types over a range of wavelengths. Dichroic shortpass and longpass filters can also act as hot and cold mirrors respectively.  Dichroic filters can divide natural light from a certain wavelength into two parts, one of which passes through, and the other is reflected or absorbed. Filters that allow longer wavelengths of light to pass through are referred to as long wave pass filters, and filters that allow shorter wavelengths of light to pass through are referred to as short wave pass filters. The desired spectral range can be achieved by using different dichroic filters. Dichroic Longpass Filters Cut-On Wavelength Transmission Wavelength Reflection Wavelength Wavelength Range(nm) Wavefront Tolerance Material Diameter 400 420-1600 350-375 350-1600 1/4λ Fused Silica 12.5 25 450 470-1600 350-430 350-1600 1/4λ Fused Silica 12.5 25 500 520-1600 350-480 350-1600 1/4λ Fused Silica 12.5 25 550 575-1600 415-515 415-1600 1/4λ Fused Silica 12.5 25 600 625-1600 460-570 460-1600 1/4λ Fused Silica 12.5 25 650 675-1600 495-610 495-1600 1/4λ Fused Silica 12.5 25 700 725-1600 535-600 535-1600 1/4λ Fused Silica 12.5 25 750 780-1600 565-715 565-1600 1/4λ Fused Silica 12.5 25 800 830-1600 600-760 600-1600 1/4λ Fused Silica 12.5 25 850 880-1600 635-805 635-1600 1/4λ Fused Silica 12.5 25 900 935-1600 675-855 675-1600 1/4λ Fused Silica 12.5 25 Dichroic Shortpass Filters Dichroic Shortpass Filters Cut-Off Wavelength Transmission Wavelength Reflection Wavelength Wavelength Range(nm) Wavefront Tolerance Material Diameter 400 325-385 420-485 325-485 1/4λ Fused Silica 12.5 25 450 325-430 470-545 325-545 1/4λ Fused Silica 12.5 25 500 325-480 520-610 325-610 1/4λ Fused Silica 12.5 25 550 400-530 575-725 400-725 1/4λ Fused Silica 12.5 25 600 400-580 625-795 400-795 1/4λ Fused Silica 12.5 25 650 400-630 675-850 400-850 1/4λ Fused Silica 12.5 25 700 400-680 725-990 400-990 1/4λ Fused Silica 12.5 25 750 400-725 800-990 400-990 1/4λ Fused Silica 12.5 25 800 400-775 850-1050 400-1050 1/4λ Fused Silica 12.5 25 850 880-1600 635-805 635-1600 1/4λ Fused Silica 12.5 25 900 400-820 910-1110 400-1110 1/4λ Fused Silica 12.5 25

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

Dichroic Longpass Filters Cut-On Wavelength Transmission Wavelength Reflection Wavelength Wavelength Range(nm) Wavefront Tolerance Material Diameter 400 420-1600 350-375 350-1600 1/4λ Fused Silica 12.5 25 450 470-1600 350-430 350-1600 1/4λ Fused Silica 12.5 25 500 520-1600 350-480 350-1600 1/4λ Fused Silica 12.5 25 550 575-1600 415-515 415-1600 1/4λ Fused Silica 12.5 25 600 625-1600 460-570 460-1600 1/4λ Fused Silica 12.5 25 650 675-1600 495-610 495-1600 1/4λ Fused Silica 12.5 25 700 725-1600 535-600 535-1600 1/4λ Fused Silica 12.5 25 750 780-1600 565-715 565-1600 1/4λ Fused Silica 12.5 25 800 830-1600 600-760 600-1600 1/4λ Fused Silica 12.5 25 850 880-1600 635-805 635-1600 1/4λ Fused Silica 12.5 25 900 935-1600 675-855 675-1600 1/4λ Fused Silica 12.5 25

Dichroic filters can divide natural light from a certain wavelength into two parts, one of which passes through, and the other is reflected or absorbed. Filters that allow longer wavelengths of light to pass through are referred to as long wave pass filters, and filters that allow shorter wavelengths of light to pass through are referred to as short wave pass filters.

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