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Is it possible for a hobbyist to create/mold/grind/polish a lens element?

There seems to be lots of astronomy hobbyists polishing mirrors and occasionally a large lens element. Is there an equivalent hobby of creating (very rudimentary-quality) element or objective lenses for photography? I couldn't Google up any good info on this.

The Kodak Brownie was single-element and manufactured quite cheaply. What would it take to make something like that? What would be the simplest and/or cheapest way?

(Yes, I do know this is not practical. Yes, I could just strip old objective lenses. And yes, I do know the quality would be quite low.)

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While you're talking about creating the elements themselves, so this isn't an answer, I found this blog post on building lenses with cheap or scavenged elements to be very interesting. –  mattdm May 28 '12 at 0:04
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Can you link to astro folks making lenses? I know lots about mirrors there, but they're very different beasts. –  rfusca May 28 '12 at 2:30
    
The manufacture of a lens element that is pure enough to be used for photography is pretty complex. You need materials with adequate purity, light transmission, and hardness, not to mention a fair bit of precision in your grinding mechanism to ensure you refract light enough to focus it where you want it focused, and do so evenly across the surface of the lens. Even on an amateur level, it would be pretty expensive to do. This video might be insightful regarding lens manufacture: youtube.com/watch?v=OkWsk9rXpcU –  jrista May 28 '12 at 2:49
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2 Answers

I can't address your question with personal experience, but the astronomy hobbyists get very good results. They not only polish their lenses, but they make them from a flat piece of glass.

Its hard to see why you would not be able to do it. it may take a lot of time, and as you suggest, its not economical, but this is a hobby. I say go for it if you have the interest.

I suggest you read Roger's Cicala blog, he has written a lot on the history of various lens designs. http://www.lensrentals.com/blog

As far as I can tell, a lens is a lens and doesn't know if you are pointing it at a star or a pretty face.

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Note that amateur astronomers routinely grind their own mirrors, not lenses. With a mirror, the interior condition of the glass doesn't matter--it's just a mechanical substrate to hold the aluminum. –  coneslayer May 27 '12 at 20:38
    
Ah ah, thanks for the correction –  Pat Farrell May 28 '12 at 4:33
    
they could make lenses just as easily as mirrors, given the availability of the raw materials. I have made optical lenses for scientific instruments by modifying lenses for eyeglasses for example. While that project didn't require the quality glass needed for a $1000+ Nikkor, just windowpane wouldn't do either. –  jwenting Nov 7 '12 at 11:55
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There are separate issues.

  1. "Create" a lens - let's interpret that to be a design act - designing the curve according to focal length, required dispersion, etc. Yes, that's doable. There's lens design software around that will take a set of optimization criteria and some constraints and spit out a set of curves and glass types. Rustle up specific software recommendations on the amateur telescope making lists, I know I've seen them there.
  2. Mold a lens - not without herculean effort. The homogeneity required of optical glass is, according to every thread on the topic I've been able to find, pretty much out of reach for garage tinkerer types. This isn't to permanently dissuade you from trying - I'd love few things more than to see another "you can't do this at home" techno-cultural touchstone falling. But you'll have to get (and maintain!) sufficiently transmissive glass, of sufficiently controlled optical parameters (index of refraction, dispersion), completely free of bubbles, and completely homogeneous. These are partially conflicting requirements, as it's difficult to, for example, have a thoroughly homogeneous melt without stirring, which can easily introduce bubbles.
  3. Grind a lens - Definitely. I can't find the link now, but I saw an argument once that grinding (and, by extension, polishing) a good lens is easier than grinding a mirror, since the curves for a given f ratio are steeper with a lens, so errors show up more prominently during testing.
  4. Polishing a lens - Yes again, as at this point it's the same as polishing a mirror surface, except perhaps for the steeper curve. Figuring an aspherical lens surface might be harder than figuring an aspherical mirror surface, for the same reason testing a lens is easier: the curves are steeper on a lens, so the lap has to flow a lot more as it mates to the lens in various positions.

Disclaimer: This is mostly book-knowledge, not so much hands-on knowledge. While I've ground and just started polishing a small mirror, I've never tried making a lens.

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