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Thread: Lens spacing

  1. #1

    Lens spacing

    Hi!

    When mounting a lens into a shutter, the spacing of the front and rear cells may have to be adjusted in relationship to each other and to the aperture plane by means of thin spacing rings (shims). How exactly is this measured, and which instruments does it require?

    It is not that I want to do it myself. The background:
    On a norwegian photo forum, I asked who here in Norway might be able to mount a lens into a shutter. (A taking lens into a fitting shutter, not the adapting of a barrel lens.) I was referred to the former Sinar representative. I called him and he said yes. But when I detailed my question to include the spacing, the answer changed into no.
    When I asked who could, he said that they had sent lenses to Schneider in such cases. But while Schneider may be willing to deal with an Angulon, they may not be thrilled about an Apo Ronar or an A Fujinon. Also, in order to keep shipping cost down, I would prefer to send all the stuff to one and the same address.

    So, when I try to find somebody else, I feel I have to ask how exactly they do it, and if they have the tools required.

    Grimes probably has, but they don't answer my e-mails.

    Good light - Hening.
    Hening

  2. #2

    Join Date
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    Lens spacing

    Hi Hening, whenever I needed something done from SK Grimes I called them and always got an answer - I think they are overwhelmed with orders and just don't get around answering email. Why don't you give them a call - I am sure they'll be able to do the job for you.
    Juergen

  3. #3

    Lens spacing

    Second the S K Grimes.com

  4. #4
    Donald Qualls's Avatar
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    Lens spacing

    I've actually gotten e-mail replies from Grimes recently, inquiring about retaining rings vs. flanges (and getting good news on pricing, I might add -- I was fortunate to find the shutters I own without rings have standard #0 threads). Might need to include suitable keywords in the subject to keep your e-mail out of the spam bin...

    Meantime, however, ISTM that you'd significantly change the focal length if the element spacing were incorrect. Am I correct in thinking the glass you have is already in cells, and that the cells match the threads in the shutter you wish to use? If so, you should be able to simply screw them in snugly, check that the focal length (from aperture to film plane) is within about 2% of the figure engraved on the name ring, and go take pictures -- they'll normally already have any shims they require inside the threaded cells, which were made to provide correct element spacing when installed in a standard shutter (assuming, at least, that all components were made after about 1930).
    If a contact print at arm's length is too small to see, you need a bigger camera. :D

  5. #5

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    Lens spacing

    Hello,

    I had lens cells that I tried to have mounted to a shutter. It can be a difficult and expense job. The spacing is important, and can be critical for some lens cells. I believe SK Grimes can do it, but I think only if the cells are currently mounted, either in a shutter or barrel, and the proper spacing can be determined from the existing mount. They did not believe they could do it properly for my Dagor cells without an exsisting mount.

  6. #6

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    Lens spacing

    My feeling was similar to Donald's ; I clearly remember a French LF tutorial book of the seventies stating that view camera lenses were designed to be relatively insensitive to mis-spacing in order to make the exchange of lensboards easy with simple tools.

    This, until I read this notice on the official Schneider Kreuznach web site.
    www.schneider-kreuznach.com/service/service_e.htm


    * Our ranges Super-Angulon (incl. XL types), Super-Symmar XL, Super-Symmar HM, Apo-Componon and Digitar can be only repaired at Schneider-Kreuznach. To optimize the optical parameter in the best possible way an exact re-adjustment of these lenses after repair is absolutely necessary.

    * Complete shutters should be only exchanged by Schneider Kreuznach directly (also here re-adjustment).


    My conclusion is simple.
    You can do what you wish with older standard and long focal lengths. Dissassemble. Swap boards. Swap shutters. Remount. Adapt. And forget about shims.

    But for modern wide angle lenses, any kind & any manufacturer, the most critical lenses being ultra-wide angle and 'digital' series, do it at your own "risk" if you believe in what Schneider Kreuznach people officially post on their web site.

    To me this is the price you have to pay for the improved performance between and old 'not-super' Angulon(TM) and a brand new super-aspherical-wide-top-notch ;-);-)

  7. #7

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    Lens spacing

    I had a lens that needed a new shutter a couple of years ago. My question, to myself, was that with old lens/shutter combinations, how would anyone know if the spacing was correct to begin with???

    I asked a lot of people... No one knew the answer....

    I asked Grimes about the re-mounting and measuring the spacing. Their answer was simple. If it focuses at infinity, don't worry about the spacing! If it doesn't focus at infinity, they send it out to an optics shop to have it measured on an optical bench, at considerable cost....

    Luckily, I found a shutter. The spacing was off from the 'original' by a mm or two. I tried the lens at infinity and closer and could see absolutely no difference (switching between shutters). So I just kept it in the new shhutter and was happy...

    As was said, some of the modern lenses might have trouble. Like many things in LF, do it and see what it looks like.... Maybe you'll be as lucky as me?

  8. #8

    Lens spacing

    Many thanks to all of you who responded!

    Parallel to my question here, I asked Tim Sharkey from lensN2shutter.com, who has been very responsive to e-mails all the way, and here is his answer:

    "If you have the factory barrel, I have the tools to measure and properly space the groups from the shutter. If you only have the lens groups by themselves, the only way to get the proper placement of the cells without the factory barrel would be on an optical bench with an autocollimator. I am in the market for one of these tools but have not purchased one yet."

    To Donald: Yes the lenses are in cells, and the threads fit in the shutters (not tried yet for the Angulon 65 though).
    - "they'll normally already have any shims they require inside the threaded cells" - I had read about these shims before, but had never seen one when I unscrewed a lens from a shutter. But I have just acquired a like-new Apo-Sironar S 135, and this one has a shim. This thing is *very* thin indeed...

    The lenses are an Angulon 65, which I want to move from the Prontor SVS #00 shutter, in which I bought it, into a Compur 00 which I acquired later; an A Fujinon 9/180 purchased used from Adorama for 274 $, which came in an odd model of a Copal 0, and with an f-stop scale starting at 5.6, so this is obviously not the original shutter; and maybe an old, single-coated Apo-Ronar 300, of which I have the orphaned cells, which are in brass. (The cells alone weigh 125 grams; would anybody know the weight of a modern Apo Ronar 300 in aluminum mount?)

    Good light! - Hening.
    Hening

  9. #9

    Lens spacing



    Hening, with the three older lenses that you described, I would just transfer the cells to new shutters and then take test photographs.





    The adjustment shims that I have seen in some modern lenses are between the front cells and the shutter. (Shims are placed on the front because the user is less likely to damage them -- the rear cell generally must be removed to install the lens onto a lensboard.)
    It seems that the manfacturers are adjusting the spacing between the front and back cells to compensate for some variations.
    The crucial question is whether they are compensating for variations in the power of the lens cells or in the thickness of the shutters. If the shims are because of variations in the lens cells, then there shouldn't be any difficulty in transfering the cells to a different shutter. If the variations in shutters matter, then a different thickness shim might required for a different shutter. Copal provides specs on the accuracy of their shutters, e.g., 0.025 mm (= 0.001 inch) for the thickness of a #1 Press shutter.





    Of course one shouldn't go wrong with sending a Schneider lens to Schneider. The question is whether it is necessary, or whether Schneider is trying to increase their repair business. When you buy a new car, typically the manufacturer will assert that all repairs should be done at the dealer by factory authorized technicians. Do you always take your car to the dealer, or to an independent repair place? It would be nice if Scheider stated a accuracy requirement, e.g., lens cell spacing must be maintained to 0.01 mm accuracy.





    Does anyone know of patents on some of these modern lenses? They might answer the accuracy questions, at least if someone did a computer analysis with different spacings.





    A previous discussion: Interchanging lenses in Copal Shutters. Why does it work? at http://www.largeformatphotography.in...ic/498712.html.


  10. #10

    Lens spacing

    Hening, The spacing between cells can be very critical to optical performance. Generaly the better corrected the lens design the more sensitive it is to the central airspace distance. Kingslake discusses this in his book ,"A History of the Photographic Lens" (1989 , pp6-7). He states that in a DAGOR a small error as little as 0.4% has a considerable effect on field curvature, and a lesser effect on coma. For example 0.4% of 65mm would be 0.26 mm, or about two sheets of thin copy paper.

    I (think??) remember reading a lens test of a DAGOR where the tester rotated (unscrewed) one of the cells (~ 45 degrees ), and noticed a large degredation in lens performance. However the tester wrongly attributed it to problems in optical centering.

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