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How do I arrange optics to make a decent periscope? Answered

Ever since I watched the first season of Stargate SG1, I've wanted one of those sweet little tactical periscopes that Jack o'Neill uses to look around corners to avoid Jaffa. The image is here, but it's just a prop! As far as I can tell, they either don't exist or are absurdly expensive or are just really hard to find. So I want to make one. I know some basic optics from working in a university laser lab, but we don't usually use lenses and such. I have played with simple two-lens telescopes and know that the ratio of the focal lengths is the amount by which an image is magnified. The corner would need to have a tiny prism in it.

The problem I'm having is this:
If I use tiny lenses, and a longish (~30cm) tube, the viewable area is ridiculously small. I would love to find a way to enlarge the viewable area I see in the eyepiece. Does anyone here know how this is done? At the very least I would like to know how to position the optics so that it seems like my eye is at the far end of the periscope. Maybe I could use a peephole lens to get a wider field of view too.

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steveastrouk
steveastrouk

Best Answer 8 years ago

From Wikipedia
http://en.wikipedia.org/wiki/File:Periskop_linsen.svg

Its done with "relay lenses" down the tube. The relay lenses are used to collimate the light from one end, pass it down the tube, and then refocus it.

I have a friend who built BIG binoculars from a set of 12" periscope optics AFAIR, they were 10 feet long !!

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laserjocky
laserjocky

Answer 8 years ago

This is probably what I need, but that diagram is scary. Especially the part about the field lens, which apparently can cost upwards of 1000USD. Maybe I can find a way to do it crudely with a single lens. But I need to figure out how to calculate the focal lengths I need.

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steveastrouk
steveastrouk

Answer 8 years ago

Just look on line at "Surplus Shed" - Fred'll have what you need.

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laserjocky
laserjocky

Answer 8 years ago

That site is the motherlode. I've been trying to find a good place to buy random lenses for a long time. You, sir, win the best answer award.

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iceng
iceng

Answer 8 years ago


Great Link :)

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steveastrouk
steveastrouk

Answer 8 years ago

You're in the right place to get your hands on a student copy of OSLO.....but that might be overkill......

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iceng
iceng

8 years ago

I would suggest a front surface mirror in place of the rt-angle prisms
as that will transfer more of the light then glass.
How much can you see through a 15" long 1/2" tube anyway.

The periscope in modern day is an image intensifier system.

Optical Telescopes use a large light gathering lens in front

A

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laserjocky
laserjocky

Answer 8 years ago

That's exactly my problem though, seeing THROUGH a long thing pipe doesn't do much good. There must be a way of producing an image that is not only magnified, but is also angularly large. I'm having trouble wrestling with the idea that all the light collected at the objective lens is beamed to the eyepiece in a simple 1:1 telescope, but the viewable image area is negatively impacted by having long focal lengths.

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rickharris
rickharris

8 years ago

Web cam at the end and a net book at the other - Simple.

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laserjocky
laserjocky

Answer 8 years ago

I was considering this method. I'd love to find a way to do this with traditional optics though.

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iceng
iceng

Answer 8 years ago

Aha a modern periscope.

I would add one mirror in the front,
For easy replacement from bullet damage.

Just as tank driver slits are mirrors with drop in replacements.