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How to make an old opaque projector focus at a closer distance? ? Answered

I recently pulled a fully functional Seerite 10x10 opaque projector from a dumpster, but it only focuses at ~ 15-18 feet from the surface that I am projecting on; any way to shorten the focal distance?

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KellyCraig (author)2013-10-12

I just use an old oatmeal tube to extend the lens out farther. It's worked for about thirty years. Of course, you need to support the tube, but that isn't usually a problem.

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KellyCraig (author)KellyCraig2013-10-12

Sorry, didn't note the fact the lens appeared stuck. For one of my units, you just loosen a know and slide the lens in or out. For another, you loosen a knob and turn it. There is a spiral cut in the lens housing and it allows the screw to move closer or farther from the body, changing the focal point.

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steveastrouk (author)2012-06-13

Add a low power convex lens, ideally a doublet. Try
http://www.surplusshed.com

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A.J.B. (author)steveastrouk2012-06-15

Is there a way I can just make the existing lens focus at a closer distance? Does the little plastic screw on top do anything?

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steveastrouk (author)A.J.B.2012-06-16

Yes, it allows the front lens to be slid in and out !! You didn't SAY that you had a focussing option !

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A.J.B. (author)steveastrouk2012-06-16

Sorry, I didn't realize that is what it was. I tried tightening and loosening the screw, but nothing seemed to change...? Do I just unscrew it and manually push/pull the lens in or out?

Also, thank you for your patience with my complete lack of understanding on this. I've used analog cameras, digital cameras, microscopes, etc, but all the while, I've come to realize that I know nothing about the actual function or science of optics. I am used to just turning the ring on a camera lens to focus it.

Also, I have searched google for hours, apparently this size/model is pretty rare, so no documentation to be found anywhere.

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steveastrouk (author)A.J.B.2012-06-16

Yes, try pushing and pulling the lens - though, has this thing been painted do you think ?

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A.J.B. (author)steveastrouk2012-06-21

So I finally got around to trying the pushing/pulling, no dice. It seems pretty secure in there, and the force I was putting on it seemed a bit excessive. I got sidetracked by my first instructable, but I think I'll go at the lens from the inside sometime this weekend, I just need to figure out how to deconstruct the case.

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steveastrouk (author)A.J.B.2012-06-21

Try wiping a bit of WD40 on the outside - don't spray it, it'll mess things right up. Then try it tomorrow.

Steve

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A.J.B. (author)steveastrouk2012-06-16

Pretty sure it's just the original manufacturer's paint. There is some kind of silver fabric around the lens edge, which would probably make it easy to slide in or out. At work right now, but I will try it when I get home. This will be awesome and much easier if it works!

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A.J.B. (author)steveastrouk2012-06-15

I'm not very familiar with optics. Would I attach the lens in front of/behind the existing one, or just replace it? Forgive my ignorance.

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A.J.B. (author)steveastrouk2012-06-15

Also, I have several old lenses, 25mm-150mm for an old analog camera. I was thinking I could somehow add one of these in-line and be able to change the focal distance. Is this possible?

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