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Thread: Process lens image circle nature

  1. #1

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    Process lens image circle nature

    I am planning to buy my first large process lens and I am wondering how does various process lenses image circle behave. Is it quick cut off or more gradual fade?

    I am considering something around 750-800mm range and I plan to use it for portraiture (i.e. 1:1).

  2. #2
    Tin Can's Avatar
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    Re: Process lens image circle nature

    Depends on magnification and format

    I have a 900mm Jena and it needs a lot of bellows for a head on 11x14

    Tell us your plan
    sin eater

  3. #3
    Drew Wiley
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    Re: Process lens image circle nature

    Officially published image circles for process lenses are geared to very high quality apochromatic standards and tight dot reproduction right out to the corners. Therefore these figures are far more conservative than those used for ordinary photography. They might be rated at infinity as well as for 1:1, but frequently at f/22. So you have a number of variables to contend with. But you must be dealing with an enormous piece of film if you're worried about image circles for process lenses that long. The 780 Apo Nikkor I have was used on a process camera, max 22 feet long and equipped pin-registered for 30x40 inch repro film. The way you are probably contemplating using a process lens, straight on, even a 305 would easily cover 8x10 film corner to corner without any falloff or sacrifice of precision, even by f/11. A 240 does it by f/16. Gradual fade isn't in process lens vocabulary; it would be unacceptable except in cheaper process lenses like those used in old Stat cameras and T-shirt silkscreening shops. But if you intend to use something around 700mm at 1:1, you must have an awfully long bellows yourself!

  4. #4

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    Re: Process lens image circle nature

    Quote Originally Posted by erian View Post
    I am planning to buy my first large process lens and I am wondering how does various process lenses image circle behave. Is it quick cut off or more gradual fade?

    I am considering something around 750-800mm range and I plan to use it for portraiture (i.e. 1:1).
    I think you're asking about illumination, not about image quality. Long process lenses such as you mentioned all cover relatively narrow angles. For example, the 750/9 Apo-Nikkor (tessar type) covers 37 degrees (500 mm @ infinity, 1,000 mm @ 1:1) and the 760/11 Apo-Nikkor (dialyte type) covers 42 degrees (600 mm @ infinity, 1,200 mm @ 1:1). At 17.5 degrees off axis, cos^4 reduces illumination by no quite 1/4 stop. At 21 degrees off axis, less than 1/3 stop. Stop worrying.

    To echo Mr. Wiley, if you must worry, worry about how you're going to get the extension needed to shoot at 1:1 with such lenses.

  5. #5

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    Re: Process lens image circle nature

    Quote Originally Posted by Tin Can View Post
    Depends on magnification and format

    I have a 900mm Jena and it needs a lot of bellows for a head on 11x14

    Tell us your plan
    I plan to build a camera obscura. The one where you can walk in. I plan to focus by moving the back inside the camera. I am thinking to use large photo paper and by large I mean really large like 1 meter by 60 cm or similar.

  6. #6

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    Re: Process lens image circle nature

    Quote Originally Posted by Dan Fromm View Post
    To echo Mr. Wiley, if you must worry, worry about how you're going to get the extension needed to shoot at 1:1 with such lenses.
    I am not worrying about the bellows because I do not plan to use them. The idea is to build a walk in camera obscura.

  7. #7

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    Re: Process lens image circle nature

    Good day to all of you

    This has been discussed on here before (possibly on a slightly different basis):

    https://www.largeformatphotography.i...-Lens-Database

    which may or may not help the OP

    rgds

    Andrew

  8. #8

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    Re: Process lens image circle nature

    Quote Originally Posted by erian View Post
    I plan to build a camera obscura. The one where you can walk in. I plan to focus by moving the back inside the camera. I am thinking to use large photo paper and by large I mean really large like 1 meter by 60 cm or similar.
    How will you keep the paper plane perpendicular to the lens' axis?

  9. #9
    Tin Can's Avatar
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    Re: Process lens image circle nature

    Many people have done this, which doesn't mean don't do it. It's huge fun! I did it a few years ago and plan to do it better next year.

    Read this https://www.largeformatphotography.i...l=1#post874269

    Then this, I have the 790mm http://re-inventedphotoequip.com/Formats.html

    Some just sit inside and look. https://www.vice.com/en_us/article/x...scura-brooklyn

    Other's make big wet plates https://www.ianruhter.com/

    Largest print ever made https://en.wikipedia.org/wiki/The_Great_Picture

    Soft or sharp edges I cannot say as I never worried about that.
    sin eater

  10. #10

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    Re: Process lens image circle nature

    Quote Originally Posted by Dan Fromm View Post
    How will you keep the paper plane perpendicular to the lens' axis?
    A solution would be placing a toy laser in the lens board (well perpendicular to the lens board!) and then placing a piece of mirror on the paper plane, or the counter, the laser on the paper and the mirror on a filter mount.

    The laser refrigerator base I've it is perfectly perpendicular to the axis, I use that to align the enlarger, but it should work perfectly in that application...

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