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How to limit light thru magnifying glass Answered

I'll try to make this short and to the point - Does anyone know a way (or could think of a way) to make a device that would fit onto a magnifying glass or similar, so when the magnifying glass is used to burn wood/start fires, the burn mark is not as thick? Thanks.



10 years ago

Thank you everyone who has answered, next sunny day that comes up I will try out the methods I can that y'all have posted. Thank you!

OK, this needs an instructable - some device that focuses a magnifying lens into a light-pipe, allowing the light to be used more conveniently for pyrography or solar soldering, like the bendy extension of a rotary tool.

Fibre optics don't carry heat, just light (that's why they're used for cold lighting. A light-pipe is a hollow tube with a reflective inner surface - acts just like an optical fibre, but it will carry heat as well.

Fiber optics are most often used to carry infrared light, which is associated with heat. My electric stove lights up on my IR night vision camera for example. Since magnifying glasses do not get hot while in use for burning, nor do they have a pipe like structure to hold hot air in, it doesn't matter if fiber doesn't "carry heat". I do think it's possible that if you focused a magnifying glass on a fiber optic cable end, it might get hot carrying so much light, especially IR, just like a wire gets hot if it carries too much current. And if the fiber remains cold, and if most of the light that goes in comes out the other side, it should burn things as well as the magnifying glass, as if the light went thru the air instead of the fiber or lightpipe. Where is fiber used for "cold lighting"? I suppose if the light source is an incandescent bulb, I agree that the heat from hot air around the bulb doesn't go through the fiber.

"Cold" lighting is used when surgereons need a bright light to see a small area in detail. Rather than illuminate the area with close, hot bulbs (the heat damages delicate tissues), they use fibre optics to guide the light in from a distance.

Oh, sorry---I misread your post. I thought you just wanted light.

Try a second, smaller magnifying glass to focus the light from the first. It could be set up in a tube, or just use both hands : )

Years ago I was at a couple of street fair / art faires in the SF south bay area, there was a guy who created "drawings" on wood using a magnifying glass. Seems like he had more than one depending on how soft or deep he wanted to burn the image. It would start smoking, he would pull the lens away, wipe it, burn some more. Solar wood burning. Regular old high quality magnifying glass as has already been mentioned here.

Good focus. Good alignment. The lens wants to be aligned directly with the sun. One thing you can to is to cast a shadow with e.g. a carboard tube, and adjust the tube until you have a perfect ring of shadow: the tube is aligned correctly with the sun. If you can mount both the lens and tube on a tripod, it's much easier (I should have photographed that, maybe some other sunny day...) L

Basically you want the resolution of the burnt marks reduced..right? Im not really sure..but i think if you focus the light from a larger magnifying glass onto a smaller one, the focal point will get smaller and smaller.. You can also try CD-ROM lense.. All the best..


11 years ago

Like Cameron said you need a quality magnifing glass. You could simple just focus it and turn it so its parallel to the sun

I believe that you are asking if there is a device that would reduce the diameter of the burn mark. The answer is a better magnifying glass. A "perfect" lens, meaning one free of any anomalous refractive properties, would transmit 100% of the light through the lens and could concentrate it to an infinitesimal point. However, perfection is impossible, so magnifying glasses transmits most of the light and concentrate it to a fairly small blob. The higher the quality of the glass itself and the shaping process, the smaller the point that light is concentrated to. You could correct misshapen lenses, like was done to the spherical aberration that screwed up Hubble's primary mirror, but that would require incredibly precise measurements and incredibly precisely made corrective optics. It's easier to get a better lens.