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Could I build a giant magnifying glass? (And maybe incorporate it into a steam engine?) Answered

Optics are fun, and so following that logic, scaled up optics should be even more fun. And so this leads us to: How do I build a giant magnifying glass?


The sun has a lot of power, and I want to harness that energy, and try out a few things, including the interesting prospect of using it to power a steam engine. (Heat up something, run water over it, and run the steam through a turbine).

Several methods have come to mind, including: acrylic, freezing some water in specially-shaped bowls, and sandwiching water (which has a slightly higher refractive index than ice) between two parabolic pieces of plastic. I'm personally concentrating on the last one, as it would be more permanent than the ice.

Just thought this up: freezing a lens, and then coating it with something immediately so that it will stay once it melts. What do we have that is clear, dries quickly, and readily available?

Does anybody else have experience with this?

UPDATE: Some relevant links...
An ideal result.
Parabolic mirrors are another possibility, but I'm still more interested in a lens.
Where a lot of this sprang from.
Indices of refraction. Is it Indices or Indexes?
Hmmm....

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Jezza Bear (author)2007-03-15

I know it is not a lens but my site has this (it was an old Instructable here before I deleted it)Solar Kettle.

I have burnt my fingers with this!

I think I have seen articles on Ice lenses, not very good I am afraid , very difficult to get the curve

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carbon (author)Jezza Bear2007-03-15

Is it really that hard to get the right curve? I see it as just a matter of getting the right bowl-shaped thingy to put the water in.

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Kiteman (author)carbon2007-03-15

It has to be a smooth curve.

I'd be more inclined to try fresnel lenses. You can buy quite large examples, but I have a couple (just over a foot across) that came off old OHPs since my school went digital. I'm just waiting for a lighter, sunny evening to try and set fire to something...

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lemonie (author)Kiteman2007-04-01

Would a lighthouse-clearance lens be any good? I only ask (out of curiosity) because of the size of the things.

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Kiteman (author)lemonie2007-04-02

You have a light-house lens??? How big is it? You must be able to melt metal with one of those!

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lemonie (author)Kiteman2007-04-02

No, but since I occasionally see big lenses like this I'm curious to know whether there would be any value in buying one.

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Kiteman (author)lemonie2007-04-02

Certainly an awful lot of play value...

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carbon (author)Kiteman2007-04-01

I found a 1.5 ft. by 1.5 ft. Fresnel lens at a podunk hardware store. (From what I understand, it gets mounted in the rear window so truckers can see where they're backing up). It's a flexible sheet of plastic, by the way. I stashed it behind a shelf so I can come back later and buy it. ; )

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carbon (author)Kiteman2007-04-01

In an overhead, is the lens solid or just a flexible sheet? Do the lenses you have focus light down to any sort of a point? Or do they have a pretty broad focus point?

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carbon (author)Kiteman2007-03-15

Smooth like not rough, or smooth like one continuous curve?

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zachninme (author)carbon2007-03-15

I saw a 4ft x 4ft one online for $20, which is cheap :-)

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carbon (author)zachninme2007-03-15

4 by 4 ft. what, exactly?

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zachninme (author)carbon2007-03-16

Wow, sorry, I think this got tagged onto the wrong comment :P Frensnel lens, that is. WestFW's link is probably the best, I think it was a "blowout" sale I saw mine at :P

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Kiteman (author)carbon2007-03-16

Smooth like one continuous parabolic curve. Maybe stretch an elastic membrane over a circular frame and pour in water - the weight of the water will (maybe) stretch the membrane into the right curve - then freeze the whole thing. Use boiled water to cut down the cloudiness caused by air coming out of solution as it cools.

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jtobako (author)Kiteman2007-03-15

i saw someone's setup made from a projection tv, something like 4' (1.2 m?) across. they were having fun melting low temp metals (copper coated zinc pennies in seconds).

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carbon (author)Kiteman2007-03-15

Hehe, I'm actually finagling my way in next to the IT guys at my school, as they are systematically phasing out the over-head's... I'm also trying to get salvage rights / first dibs, on a planetarium projector that is being replaced by a digital one. : )

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Jezza Bear (author)carbon2007-03-16

Hey Carbon

I knew I had seen this....this is a web site of a really cool (pardon the pun) television programme we have in the UK

Rough Science

They seem to have done t using a balloon. I remember the programme when it was on air and they were not to impressed by it, but worth the experiment anyway..enjoy

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Kiteman (author)2007-03-16

If you're using solar, why not use it to drive a stirling engine instead?

http://pesn.com/2005/08/11/9600147_Edison_Stirling_largest_solar/

And I'm sure gyroscope.com does one, but their site is down at the moment. Do a google image search for solar stirling parabolic to see what I mean.

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lemonie (author)2007-03-15

I agree with JB you're best with a parabolic mirror. And old satellite dish might be an easy starting point?
You should easily power one of these(?):
http://www.mamodonline.co.uk/index.php?crn=238

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Kiteman (author)lemonie2007-03-16

My Science Clubbers once wrapped an old dish in foil and used it to melt chocolate. They documented it and won an award for their investigative skills.

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carbon (author)lemonie2007-03-15

I've never seen them that cheap! I was saving to buy one for my Dad, so thanks for the link. : )

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lemonie (author)carbon2007-03-15

Those are more advanced than the basic model I have (in bits, with worn parts...). Do you live in the UK?
Perhaps your dad might like something from here:
http://www.gyroscope.com/
(It wasn't loading for me tonight, but I'm sure it's the correct site)

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carbon (author)lemonie2007-03-15

Yeah, you seem to be right about the page being down. Anyway, I live in the States. The thing was that my dad had a steam engine when he was a kid, but he left it behind when they moved, so I'd like to get some good son points and buy him one.

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westfw (author)2007-03-16
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dogsrcool2me (author)2007-03-15

water expands when it turns to ice.

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carbon (author)dogsrcool2me2007-03-15

True, and I have anticipated this. It would be a simple matter of drilling a hole and squirting in some water, I would imagine.

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