How To Clean Your Spotting Scope - how to clean scope lens

 2024-06-15 09:32:17

Ande's hand. Actually a black leather glove she was wearing. Remember kids, don't get your hand in the beam -- that glove started smoking instantly. It seems when you are wearing #12 arc welding lenses, you can't see much short of the sun and whatever is in the lens' focus. (Like your hand on fire.) The side of someone's head. I don't even remember who's head it was. Or maybe I won't say to save that person embarrassment. But it was far enough from the focal point to do too much damage. Or at least that is the claim. A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Page contents: Historic (1995) Giant Fresnel Lens Page FAQ (including where you can get your giant fresnel lens!) The New Lens Random Destructive Acts via Focused Solar Radiation When I was a kid, I always wanted Edmund Scientific's Giant Fresnel Lens. "Melts asphalt in seconds!" the ad said. When I went to graduate school I met several other people with the same enthusiasm for aimless destruction through bizarre means, and just enough combined cash to make it happen. Thus the reign of terror began. Unfortunately since I am now in California and the beloved Dershem Memorial Lens is still in Michigan, as is most of the, er, evidence, I can not at this time provide any images. Things we have destroyed with the giant Fresnel lens: Our retinas. This lens takes nearly a square meter of sunlight and concentrates it into about a square centimeter. We did not have the lens for too long before we were all seeing spots and heading to the nearest welding supply shop. "Are you doing arc welding or gas welding?" "Neither, actually we are destroying random inanimate objects with a giant Fresnel lens." Ande's hand. Actually a black leather glove she was wearing. Remember kids, don't get your hand in the beam -- that glove started smoking instantly. It seems when you are wearing #12 arc welding lenses, you can't see much short of the sun and whatever is in the lens' focus. (Like your hand on fire.) The side of someone's head. I don't even remember who's head it was. Or maybe I won't say to save that person embarrassment. But it was far enough from the focal point to do too much damage. Or at least that is the claim. A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame. As you can see, the purchase of such a dangerous item is mostly a self-destructive act. Be warned. There are probably many more otherwise useful and productive things which have met an untimely demise through our devious misuse of science. The memories are hazy (probably because of the fumes from all the burning plastic) but as they come back I will add them here. The Random Destructive Acts FAQ Updated March 19, 2003: It has been about 8 years since I wrote this page (before 2002 the last modification date was June 30, 1995) and I still get emails about it every few days. The most frequently asked question is, "Where can I buy one?" Edmund Scientific quit making this rectangular lens a few years ago and the company split, but Edmund Industrial Optics now makes a round 35 inch diameter lens (and many smaller sizes). Last I checked it was on this page but that's likely to change. It was part number NT43-921: FRESNEL LENS 35.0" DIA and cost $224.10. Jacob Dickinson informed me that Alltronics.com sells a rectangular lens similar in size to the infamous lens we had, and a few weeks ago I got one (see below). It's thinner than the Edmund's lens we used to have and needed a frame, but it's big and about half the price of Edmund's lens. You can find it at http://www.alltronics.com/lenses.htm and it was $99 plus shipping when I looked. If you're looking for something smaller and a lot cheaper, you can often find cheap surplus (used) 12" Fresnel lenses at American Science and Surplus and Scientifics (the new owner of the Edmund Scientific Catalog) for as little as $3. And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Actually a black leather glove she was wearing. Remember kids, don't get your hand in the beam -- that glove started smoking instantly. It seems when you are wearing #12 arc welding lenses, you can't see much short of the sun and whatever is in the lens' focus. (Like your hand on fire.) The side of someone's head. I don't even remember who's head it was. Or maybe I won't say to save that person embarrassment. But it was far enough from the focal point to do too much damage. Or at least that is the claim. A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Lattice light-sheet microscopy ... Lattice light-sheet microscopy is a modified version of light sheet fluorescence microscopy that increases image acquisition ...

When I was a kid, I always wanted Edmund Scientific's Giant Fresnel Lens. "Melts asphalt in seconds!" the ad said. When I went to graduate school I met several other people with the same enthusiasm for aimless destruction through bizarre means, and just enough combined cash to make it happen. Thus the reign of terror began. Unfortunately since I am now in California and the beloved Dershem Memorial Lens is still in Michigan, as is most of the, er, evidence, I can not at this time provide any images.

Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

If you're looking for something smaller and a lot cheaper, you can often find cheap surplus (used) 12" Fresnel lenses at American Science and Surplus and Scientifics (the new owner of the Edmund Scientific Catalog) for as little as $3. And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Fresnel lenssolar concentrator

Jacob Dickinson informed me that Alltronics.com sells a rectangular lens similar in size to the infamous lens we had, and a few weeks ago I got one (see below). It's thinner than the Edmund's lens we used to have and needed a frame, but it's big and about half the price of Edmund's lens. You can find it at http://www.alltronics.com/lenses.htm and it was $99 plus shipping when I looked. If you're looking for something smaller and a lot cheaper, you can often find cheap surplus (used) 12" Fresnel lenses at American Science and Surplus and Scientifics (the new owner of the Edmund Scientific Catalog) for as little as $3. And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

One of the most powerful functions is using it as a beam deflection calculator (or beam displacement calculator). This can be as a simply supported beam or to find the deflection of a cantilever beam. Being able to add section shapes and materials, this makes it useful as a wood beam calculator or as a steel beam calculator for lvl beam or i beam design. For now, this functionality is available in SkyCiv Beam.

Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Updated March 19, 2003: It has been about 8 years since I wrote this page (before 2002 the last modification date was June 30, 1995) and I still get emails about it every few days. The most frequently asked question is, "Where can I buy one?" Edmund Scientific quit making this rectangular lens a few years ago and the company split, but Edmund Industrial Optics now makes a round 35 inch diameter lens (and many smaller sizes). Last I checked it was on this page but that's likely to change. It was part number NT43-921: FRESNEL LENS 35.0" DIA and cost $224.10. Jacob Dickinson informed me that Alltronics.com sells a rectangular lens similar in size to the infamous lens we had, and a few weeks ago I got one (see below). It's thinner than the Edmund's lens we used to have and needed a frame, but it's big and about half the price of Edmund's lens. You can find it at http://www.alltronics.com/lenses.htm and it was $99 plus shipping when I looked. If you're looking for something smaller and a lot cheaper, you can often find cheap surplus (used) 12" Fresnel lenses at American Science and Surplus and Scientifics (the new owner of the Edmund Scientific Catalog) for as little as $3. And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

It has been about 8 years since I wrote this page (before 2002 the last modification date was June 30, 1995) and I still get emails about it every few days. The most frequently asked question is, "Where can I buy one?" Edmund Scientific quit making this rectangular lens a few years ago and the company split, but Edmund Industrial Optics now makes a round 35 inch diameter lens (and many smaller sizes). Last I checked it was on this page but that's likely to change. It was part number NT43-921: FRESNEL LENS 35.0" DIA and cost $224.10. Jacob Dickinson informed me that Alltronics.com sells a rectangular lens similar in size to the infamous lens we had, and a few weeks ago I got one (see below). It's thinner than the Edmund's lens we used to have and needed a frame, but it's big and about half the price of Edmund's lens. You can find it at http://www.alltronics.com/lenses.htm and it was $99 plus shipping when I looked. If you're looking for something smaller and a lot cheaper, you can often find cheap surplus (used) 12" Fresnel lenses at American Science and Surplus and Scientifics (the new owner of the Edmund Scientific Catalog) for as little as $3. And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

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I don't even remember who's head it was. Or maybe I won't say to save that person embarrassment. But it was far enough from the focal point to do too much damage. Or at least that is the claim. A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

This lens takes nearly a square meter of sunlight and concentrates it into about a square centimeter. We did not have the lens for too long before we were all seeing spots and heading to the nearest welding supply shop. "Are you doing arc welding or gas welding?" "Neither, actually we are destroying random inanimate objects with a giant Fresnel lens." Ande's hand. Actually a black leather glove she was wearing. Remember kids, don't get your hand in the beam -- that glove started smoking instantly. It seems when you are wearing #12 arc welding lenses, you can't see much short of the sun and whatever is in the lens' focus. (Like your hand on fire.) The side of someone's head. I don't even remember who's head it was. Or maybe I won't say to save that person embarrassment. But it was far enough from the focal point to do too much damage. Or at least that is the claim. A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

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The Random Destructive Acts FAQ Updated March 19, 2003: It has been about 8 years since I wrote this page (before 2002 the last modification date was June 30, 1995) and I still get emails about it every few days. The most frequently asked question is, "Where can I buy one?" Edmund Scientific quit making this rectangular lens a few years ago and the company split, but Edmund Industrial Optics now makes a round 35 inch diameter lens (and many smaller sizes). Last I checked it was on this page but that's likely to change. It was part number NT43-921: FRESNEL LENS 35.0" DIA and cost $224.10. Jacob Dickinson informed me that Alltronics.com sells a rectangular lens similar in size to the infamous lens we had, and a few weeks ago I got one (see below). It's thinner than the Edmund's lens we used to have and needed a frame, but it's big and about half the price of Edmund's lens. You can find it at http://www.alltronics.com/lenses.htm and it was $99 plus shipping when I looked. If you're looking for something smaller and a lot cheaper, you can often find cheap surplus (used) 12" Fresnel lenses at American Science and Surplus and Scientifics (the new owner of the Edmund Scientific Catalog) for as little as $3. And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Unfortunately since I am now in California and the beloved Dershem Memorial Lens is still in Michigan, as is most of the, er, evidence, I can not at this time provide any images.

There are probably many more otherwise useful and productive things which have met an untimely demise through our devious misuse of science. The memories are hazy (probably because of the fumes from all the burning plastic) but as they come back I will add them here.

It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

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A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Use the table above to view and delete the beam length, supports and added loads. Any changes made will automatically re-draw the free body diagram of your simply supported or cantilever beam. The beam reaction calculator and Bending Moment Calculations will be run once the "Solve" button is hit and will automatically generate the Shear and Bending Moment Diagrams. You can also click the individual elements of this lvl beam calculator to edit the model.

The side of someone's head. I don't even remember who's head it was. Or maybe I won't say to save that person embarrassment. But it was far enough from the focal point to do too much damage. Or at least that is the claim. A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

Random Destructive Acts via Focused Solar Radiation When I was a kid, I always wanted Edmund Scientific's Giant Fresnel Lens. "Melts asphalt in seconds!" the ad said. When I went to graduate school I met several other people with the same enthusiasm for aimless destruction through bizarre means, and just enough combined cash to make it happen. Thus the reign of terror began. Unfortunately since I am now in California and the beloved Dershem Memorial Lens is still in Michigan, as is most of the, er, evidence, I can not at this time provide any images. Things we have destroyed with the giant Fresnel lens: Our retinas. This lens takes nearly a square meter of sunlight and concentrates it into about a square centimeter. We did not have the lens for too long before we were all seeing spots and heading to the nearest welding supply shop. "Are you doing arc welding or gas welding?" "Neither, actually we are destroying random inanimate objects with a giant Fresnel lens." Ande's hand. Actually a black leather glove she was wearing. Remember kids, don't get your hand in the beam -- that glove started smoking instantly. It seems when you are wearing #12 arc welding lenses, you can't see much short of the sun and whatever is in the lens' focus. (Like your hand on fire.) The side of someone's head. I don't even remember who's head it was. Or maybe I won't say to save that person embarrassment. But it was far enough from the focal point to do too much damage. Or at least that is the claim. A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame. As you can see, the purchase of such a dangerous item is mostly a self-destructive act. Be warned. There are probably many more otherwise useful and productive things which have met an untimely demise through our devious misuse of science. The memories are hazy (probably because of the fumes from all the burning plastic) but as they come back I will add them here. The Random Destructive Acts FAQ Updated March 19, 2003: It has been about 8 years since I wrote this page (before 2002 the last modification date was June 30, 1995) and I still get emails about it every few days. The most frequently asked question is, "Where can I buy one?" Edmund Scientific quit making this rectangular lens a few years ago and the company split, but Edmund Industrial Optics now makes a round 35 inch diameter lens (and many smaller sizes). Last I checked it was on this page but that's likely to change. It was part number NT43-921: FRESNEL LENS 35.0" DIA and cost $224.10. Jacob Dickinson informed me that Alltronics.com sells a rectangular lens similar in size to the infamous lens we had, and a few weeks ago I got one (see below). It's thinner than the Edmund's lens we used to have and needed a frame, but it's big and about half the price of Edmund's lens. You can find it at http://www.alltronics.com/lenses.htm and it was $99 plus shipping when I looked. If you're looking for something smaller and a lot cheaper, you can often find cheap surplus (used) 12" Fresnel lenses at American Science and Surplus and Scientifics (the new owner of the Edmund Scientific Catalog) for as little as $3. And to answer another only slightly less frequently asked question, no the beloved Dershem Memorial Lens is not for sale. We decided it would go to the first of us to get a Ph.D. (in other words, to first order we left it up to fate) and Chris Chaput was the proud winner. Thus Dr. Chris now owns the lens and (for obvious reasons) it is kept at least 1000 miles away from him at all times. People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

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Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

The above steel beam span calculator is a versatile structural engineering tool used to calculate the bending moment in a aluminium, wood or steel beam. It can also be used as an i beam load capacity calculator by using it as a bending stress or shear stress calculator. It is able to accommodate up to 2 different concentrated point loads, 2 distributed loads and 2 moments. The distributed loads can be arranged so that they are uniformly distributed loads (UDL), triangular distributed loads or trapezoidal distributed loads. All loads and moments can be of both upwards or downward direction in magnitude, which should be able to account for most common beam analysis situations. Bending Moment and Shear Force calculations may take up to 10 seconds to appear and please note you will be directed to a new page with the reactions, shear force diagram and bending moment diagram of the beam.

Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

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People also ask, "What was the area of the focus?" The best we ever got was about a centimeter across. The lens was somewhat flexible so the corners didn't tend to contribute much. A professor at U of M who had one of these said he built a frame with cross supports and was able to get more of the lens to contribute to the focus. A lot of people want to know what temperatures we achieved. It's hard to make this estimate, the real question should be how much power the lens can supply (and you can see more about this below). But in terms of estimates, we certainly melted aluminum which has a melting point of 660.37 degC. We never quite managed to melt copper with the old lens but (melting point of 1083.4 degC) but we have with the new one (see below) so I think we could have if the sidewalk had not been so fragile. Assuming a black body target and that the sun supplies 1340 W/m^2 (before atmospheric absorption) we calculated that we should be able to melt quartz (1610 degC) but in practice I don't believe we achieved temperatures that high. The New Lens Here are a few pictures of our new lens (from Alltronics.com) and our first test target. The target was (certainly past tense) a zinc penny. The copper turned into a black crust and the zinc ran out the side (that silver blob going up in these pictures). The target stage was some shale like rock we had sitting around, which would flake when heated but didn't pop and eject the target. We have since taken many targets and caused them to melt/incinerate/explode (it's a pain to clean pop off the lens) and soon I will add a few more pictures. Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

Updated 2003.03.19 slashdotted 2004.05.21 This is a copy of the original page at http://www-personal.umich.edu/~bclee/lens.html The University of Michigan will be deleting all www-personal web pages in 2012.

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A microscope objective is composed of a complex set of lenses and optics, and different objectives are designed for different imaging tasks.

A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.

Impressive as destroying a penny may seem, I estimated that we may have only managed to get maybe 10 percent of the available energy hitting the lens (roughly 1kW) into the penny: Mass of a zinc penny: 0.0025 kg Specific heat of zinc: 390 J/kgK Melting point of zinc: 419.58 degC Thus 20degC to about 420degC takes 390 J Latent heat of fusion for zinc: 1.1x10e5 J/kg Thus to melt the penny takes about 275 J We heated the liquid zinc considerably as well, but I will ignore that. Total energy in the penny: > 665 J It takes something under or around 6 seconds to melt a penny: 665 J / 6 sec gives us a lower limit of about >= 111 Watts Sunlight at the earth: 1365 W/m^2 Transmission of the earth's atmosphere: maybe 65-70% at this angle with some clouds? Area of the lens is about 1.1m^2 Power on the lens: approx. 1000 W Power to the penny >= 10.0% This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

This is likely at least a slight underestimate of the lens' output for at least a couple reasons: it was slightly cloudy and the sun was not all that high (effective transmission may have been much lower); likely a lot of the energy went into the stage instead of the target (the metal stage we used later was pretty badly warped when we were done). We hope to improve on this by making stands and will try to measure it more carefully. This is optically a better lens than the old Edmunds one (better image) and as Edmunds points out, optically better Fresnel lenses tend to be less efficient light concentrators, so maybe that's part of our problem too -- there was a nice central focus (smaller than the penny) but a lot of the light was scattered into a much larger area, at least a foot across. This may make the lens more useful for diffuse heat applications (cooking) than concentrated ones. We'll see . . . returN Return Why are you here? / What does it all mean? / bclee@umich.edu

A canadian penny. Like coupons, I think the redemption value of these is $.01 per 20, so why not destroy it? Actually we never managed to completely destroy it, as whatever we placed it on would perish long before the penny would. (Which brings me to the next entry . . .) We did completely oxidize the surface, however. A sidewalk. It seems that normal concrete will start emitting plumes of smoke just before it pops, leaving a crater about the size of a quarter, and ejecting the aforementioned canadian penny in some random direction. Kids, always wear safety goggles when playing with giant Fresnel lenses. Lots of chalk. Chalk actually burns under this thing. Aluminum cans. So do aluminum cans. They smell really bad. The floor. It is never a good idea to use the lens indoors. Mike's car. Well, not yet. But it's plastic, so it would go up in no time at all. Or maybe we could just shrink-wrap the body around the frame.