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.

Fresnel LensSheet

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

Apr 24, 2018 — The dispersion properties of the IOL are defined by the Abbe number (ranging in most designs from 35 to 60): the refractive index of optical ...

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

One of the most confusing things I encountered as a beginner photographer was the overwhelming number of different lenses on the market. The pricing ranged from hundreds to thousands, which seemed so crazy to me at the time. I couldn’t figure out what could possibly be the difference between all these lenses. Which lens is best for the type of photography I am trying to achieve, and which should I buy first?

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.

A long lens (like the 85mm, 100mm, 135mm…) will capture a smaller section of what’s in front of you and will compress the background.

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

Jun 23, 2020 — With a progressive-scan format sensor, also known as non-interlaced format, an entire image frame is acquired at a single instant in time (see ...

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.

Giant Fresnel lensdeath ray

Accès de folie, égarement, grave erreur de jugement ; absurdité : C'est une aberration de laisser les enfants jouer près de la route.

I'm More, and I'm so happy you're here. This blog a journal about my sessions, photography tips, travels,  and style. Stay a while and say hello!

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.

Giant Fresnel Lensprice

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

BuyFresnel Lenssolar concentrator

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.

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

Long lenses are my favorite to use in situations where I am trying to focus entirely on my subjects. The compression and blurry background that these lenses help create really make my clients pop off the image. These lenses are also very helpful to minimize distractions in the background and create a “cleaner” look.

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

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.

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

Highest quality firewire cables allow for transfer rates up to 400 Mbps and meet the IEEE-1394 specification. These cables allow for simple.

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.

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.

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.

A wide lens (like the 24mm or 35mm) will not only capture a wider range of what’s in front of you but also capture more of the details.

The longer the lens, the greater the compression and the blurrier the background you will be able to achieve (there are more factors to blurry backgrounds to consider, and you can read about them here).

Fresnel lens giantreddit

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

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.

by D Gunnarsson · 2008 · Cited by 16 — David Gunnarsson, Jani Tuorila, Antti Paila, Jayanta Sarkar, Erkki Thuneberg, Yuriy Makhlin, and Pertti Hakonen · Phys. Rev. Lett. 101, 256806 – ...

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.

Wide lenses are my favorite to use during indoor sessions. They give me more freedom to move around and include more of the details around my subject, which is very important for storytelling purposes. My favorite is the 35mm (or 24mm if you have a crop sensor camera). In my outdoor sessions, I love using my wide lens when I want to include more of the background (if it is pretty and worth capturing) and if I want to get close and intimate shots to include more of the situation.

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.

Fresnel lens giantcost

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

I also use longer lenses (50mm, 100mm) when I am trying to focus and capture small details like baby feet, baby noses, wedding rings, and such.

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 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

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

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

Fresnel lensmirror

Aug 29, 2023 — Dispersion, different wavelengths giving constructive interference at different angles, requires that n be a non-zero integer. Since the sine of ...

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.

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.

Using a mix of wide and long lenses will give you the option to provide a wider variety of images for your client. So I highly recommend having both options handy!

Optical Coherence Tomography (OCT) is the newest and least invasive method for imaging of the eye's internal structures. As the new standard of care, OCT has ...

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.

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 lens giantfor sale

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

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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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

by LV Foster · 1926 — The images which the microscope objective forms of the grating and its accompanying interference figures are not planes but are curved surfaces having their ...

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.

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.

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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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.