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  1. #1

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    Re-cementing lens elements question.

    There exists threads on the topic of separating and re-cementing lens elements already. But I've seen references touching of the miking of the original cement job with a micrometer so that the repair job will end up identical. So this leads me to speculate that the thickness glue film itself comes into play. So this leads me to a question which is the point of this post. And my question is: is it really all THAT important? If it is then I believe I have devised a method that ordinary people can do with the use of a drill press. Many ordinary people have at least a tabletop drill press, or access to one.
    Once a trustworthy person answers my question I am prepared to go into my idea. I can see the point of marking the edge of the lens stack before disassembly to make sure each is turned by the clock for reassembly, but once again my question is, would it not be enough to squish out the excess glue between the fingers and take whatever finished thickness you end up with? Or are these lenses ground and engineered so that the finished thickness be exact? And to what tolerance?
    Thanks.

  2. #2

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    As far as I understand, lens centration is more important than end thickness, for image quality.

    If the thickness is not the same after cementing, the end effect is to change the focal distance.

    If you change it a lot, you may have to reset the lens flange focal distance, which typically involves a shim.

    For an SLR, it may not make any difference, depending on where the new focal point ends up. e.g. if it can't focus to infinity any more, you'll likely need to move the entire lens head closer to the film, which may translate to a thinner shim.

    I don't recall the tolerances, but I would look at the lens formula 1/f = 1/d1 + 1/d2 as a guide

    regards
    Vick

  3. #3

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    For centering I intend to simply block it on 4 sides with oak letterpress furniture. The 2 projects I have presently in mind are the front sections of a 3.5 Xenotar from a Rolleiflex 3.5E, and the front pair from an older 80mm Zeiss Planar for Hasselblad.

  4. #4

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    I've done two Nikon 5cm f1.1 rangefinder lenses (the rear doublet) and one Nikkor 5.8cm f1.4 lens. Lots of fun.
    I've also repaired about three Leica M3 rangefinder prisms that separated.

    All successful.

    Vick

  5. #5
    Europan's Avatar
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    Quote Originally Posted by Tom1956 View Post
    For centering I intend to simply block it on 4 sides with oak letterpress furniture.
    Why not on three points? You know, a three-legged stool never wobbles.

  6. #6
    Mustafa Umut Sarac's Avatar
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    it is letterpress oak furniture.

  7. #7
    Ian Grant's Avatar
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    You might look on the Large format website, Steven Tribe has written about recementing lenses in a few Forum threads.

    Ian

  8. #8

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    Letterpress furniture is a set of wood blocks of various needed sizes, measured in units called points that was used in spacing of the lead type in old-style printing presses. It was used to fill out the chase so that the type could be locked in. Very accurately made and finished out of super-hard oak.

  9. #9

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    Quote Originally Posted by Tom1956 View Post
    For centering I intend to simply block it on 4 sides with oak letterpress furniture. The 2 projects I have presently in mind are the front sections of a 3.5 Xenotar from a Rolleiflex 3.5E, and the front pair from an older 80mm Zeiss Planar for Hasselblad.
    I know what letterpress furniture is. You're kidding right?

    This is what to use. You won't need the clamps though - http://www.mcmaster.com/#starrett-v-blocks/=nl80kb

  10. #10

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    Why would I be kidding? The 2 lenses are of the same diameter. Lay the doublet down flat, presuming the back lens is either flat or concave, and then block it on 4 sides. If the back lens is convex, I have an obvious problem. I haven't disassembled the lenses yet to see. Might have to make another plan. But that plan isn't going to include spending money I don't have. I always find a way.

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