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How can I find a replacement plastic lens for this toy twin reflex camera?
January 12, 2011 6:55 AM   Subscribe

How/where can I find or fabricate a replacement plastic lens for this toy twin reflex camera?

Long story short, my girlfriend was trying to put together this Otona no Kagaku kit and lost the plastic lens pieces that it came with. She's super bummed about it and I want to surprise her with a replacement (I know I could just buy another kit, but they're not cheap and it seems wasteful). The piece is featured in step 7.1 of the above link. I think I just need two identical plastic lenses slightly smaller than 1" in diameter. Any ideas how I can make or purchase the replacement lenses? Bonus points if it's in NYC...

Alternately, if I do just end up buying a new kit, what kind of fun can I have with this thing? I thought a pinhole camera would be fun to make but there must be some other fun ideas...

Thanks hivemind!
posted by johnnybeggs to Sports, Hobbies, & Recreation (6 answers total) 2 users marked this as a favorite
 
Have you thought of going to an optometrist and seeing if they could grind a glass piece to fit?
posted by parmanparman at 7:08 AM on January 12, 2011


Was going to suggest setting it up as a pinhole camera, but I see you've already got the idea down pat. How about fitting something inside the replacement? Like say, a light? Or use it as a really cool case for a usb hub?
posted by TrinsicWS at 7:28 AM on January 12, 2011


Step 7.1 is only for the viewfinder lens. You can probably use the camera just fine without it, just "shooting from the hip."
posted by Threeway Handshake at 7:52 AM on January 12, 2011


Threeway, that'd work except she lost both lenses.

I'm not sure about the optometrist, aren't those lenses pretty different?
posted by johnnybeggs at 8:01 AM on January 12, 2011


they could probably make a lens from pane glass
posted by parmanparman at 9:02 AM on January 12, 2011


parmanparman, who's "they"? Optometrists don't carry pane glass, so that's not a good solution for them.

The glass lens would need a different curvature than the plastic, adjusted for the difference in refractive index, but that's pretty unimportant if you don't know the curvature of both sides of the original lens in the first place.

This is best solved as a DIY job...

Assuming there's only one lens, and the distance from the back of the lens (where it was originally, that is*) to the film plane is easily and accurately measurable (get a micrometer with at least 0.25 mm accuracy, and take measurements until 3 in a row agree to within +/-0.25 mm), you can approximate** the ideal lens using the Lens Maker's Formula as:
R = F/(n-1)
where
R = the desired Radius of curvature of the plano-convex lens you want,
F = the Focal distance from the back of the lens to the film plane,
and n = the index of refraction of the lens material you buy.

Once upon a time, I would have sent you to Edmund Scientific for their large selection of off-the-shelf lenses, with all their pertinent stats listed. Now, however, the cheapest lenses i can find are $22. I leave it to you to find a cheap plano-convex lens with the right stats.

Remember, you want a plano-convex lens, with an outer diameter to fit the existing hole (or larger, and find a way to glue it in place on the back mounting surface), and you want to install it with the flat side facing the film.

* If this camera allows focusing, you should focus for infinity before making this measurement, and be sure the focus doesn't change during measurement.

** I'm ignoring the lens thickness correction, which is probably negligible here. As a guess, it's 1/3 of the lens thickness at its center.

To test this lens before gluing it down, put a piece of paper on the film plane, and point the camera at the sun. The sun should be sharply focused (again, with focus set at infinity).
posted by IAmBroom at 11:35 AM on January 12, 2011


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