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  1. #41

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    Quote Originally Posted by Murray@uptowngallery View Post
    2nd was trying to get inside to tighten it. I ended up unscrewing the rearmost element, a thin, short f.l. positive element, and I find what's left will probably cover 4x5 or 5x7. No idea what kind of distortion there may be, still have the gravity problem, but I would like to see how it shoots. I also wonder if with f.l. still in the original ballpark if my f/# will stay ballpark too...4.5 wide open.
    after i pulled all the elements out of my zoom, and found ones that might be useful, i started thinking "what's the best way to mount these? i sure wish i had a tube that was better than PVC pipe for them. wish i could make a something along the lines of a zoom lens...aw crap."

    i could have possibly used the actual zoom lens, minus some elements, as the lens tube. had i not thrown it away. doh!

  2. #42

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    Quote Originally Posted by semeuse View Post
    Determining the spacing of the two elements is slightly problematic without knowing the focal lengths, though I would venture a guess of about 1.5 - 2" should give you a nice telephoto. Have you seen Kingslake's "A History of the Photographic Lens?" Lots of descriptions and diagrams of all types of lenses from classics to modern (well, through the 80s, anyway).

    I have found that the foamcore from Borden (fairly cheap at arts and crafts stores) works very well for holding the elements if I cut the outside diameter slightly larger than the interior of the "barrel" and the inside diameter slightly smaller than the lens element - the compression holds the piece nicely. I have also used weatherstripping (for sealing windows) to good effect - it has the added benefit of being available with adhesive that will hold the glass.
    i haven't read that book, but http://dioptrique.info/ shows me some general arrangements, even if my french isn't very good. you've answered my question i think though: the negative element shouldn't necessarily be in contact with the front element. i'll give it a shot, and either get lucky or not. thanks!

    as for mounting them...i've been using black foamcore, probably elmer's. perhaps i need thicker or something, but the lenses don't feel secure. when you say weatherstripping, you mean like vinyl caulking stuff? are you using that in conjunction with the foamcore, or as an alternative? and how do you avoid gunking up your lens?

  3. #43

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    If you have the money, Matt, Edmund Industrial Optics, which formerly traded as Edmund Scientific, has all sorts of holders and mounts for prototyping. They also have singlets with known properties, achromatic doublets, ...

  4. #44

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    thanks dan. alas, i don't have that kind of money. if i did, i'd just follow jim galli around and buy up any brass lenses he happened to miss.

  5. #45
    semeuse's Avatar
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    Hey Matt -
    The weatherstripping I've used comes in rolls from places like Home Depot and Lowes. It is actually a foam tape - no caulking; doesn't really do a wonderful job of weatherproofing, but works for things like door bumpers and quickie lens mounts.
    Kris

  6. #46

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    Kris: oh! sorry, misunderstood you. ok, sounds interesting, i'll check it out next time i'm in the hardware store. thanks!
    -matt

  7. #47

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    Quote Originally Posted by Dan Fromm View Post
    If you have the money, Matt, Edmund Industrial Optics, which formerly traded as Edmund Scientific, has all sorts of holders and mounts for prototyping. They also have singlets with known properties, achromatic doublets, ...
    Ahh - good old Edmund Scientific - I remember pouring over their catalogs as a child. Now they've split into 2 companies - Edmund Industrial Optics and Scientifics - which unfortunately doesn't seem to have nearly as many cool items as it used to.

    Dan
    Emancipate yourselves from mental slavery;None but ourselves can free our minds. - Bob Marley

  8. #48
    Murray@uptowngallery's Avatar
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    Stuff costs more than when I was a kid too.
    Murray

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