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  1. #11
    Steve Smith's Avatar
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    Quote Originally Posted by tkamiya View Post
    Thanks but that's not fair! You have access to a nice CNC machine!! Very nicely done!!!
    It's amazing how many 'practice' or 'training' pieces I do on this machine!


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  2. #12

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    Quote Originally Posted by sepiareverb View Post
    In a related question- does the diameter of elements necessarily have any effect on coverage? I've heard that the 40/2.8 Sonnar that came with the Rollei 35RF (recent Voightlander clone) is optically the same as the Sonnar in the old Rollei 35 S/SE- yet the diameter of these elements is vastly different.
    Then they are not the same lens in a different mount.
    The size of the lens elements does matter, yes. But how (or how much) depends on the optical design.

  3. #13
    MattKing's Avatar
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    The design of the body of the lens affects this as well. I find it interesting that at least one of my Mamiya 645 lenses has a rectangular "gate" in it. I would guess this is to minimize image degrading flair.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  4. #14

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    Lenses (being round) 'throw' a round, circular image. Rectangular formats don't use parts of it, but the light in those parts still leaves the rear of the lens.
    It will bounce around, eventually landing on the film too, where it causes a lowering of contrast (at best) or nasty highlights (at worst).
    So rectangular baffles are put both on (and in) lenses and in cameras. The lens still has to produce a circle large enough to cover the full diagonal of the rectangular format.

    (There is at least one example of something similar, but somehow opposite: the first Kodak camera produced circular images, not - as we may think - because the lens didn't cover the format, but because the corners were spoiled by excessive flare. Instead of trying to get rid of the internal reflections, they just put in a circular mask.)

    The design of a body thus mostly is aimed at losing the extra, but unused light.
    Mostly, because the depth of the camera body does increase mechanical vignetting.

  5. #15

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    Quote Originally Posted by Q.G. View Post
    Then they are not the same lens in a different mount.
    The size of the lens elements does matter, yes. But how (or how much) depends on the optical design.
    Thank you- I couldn't quite wrap my head around that idea.

  6. #16
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    Quote Originally Posted by tkamiya View Post
    . If I wanted to play with these and say, make a panorama shooter, projecting to 120 film, how should I logically approach the lens selection?
    Measure the diagonal of your proposed film gate size. Select a lens with an image circle that is bigger than your measurement. So, for example if you film gate is nominal 6x12cm (actual 56mmx112mm) you should look for a lens with an image circle 125mm or greater.

    The size of the glass is not always related to coverage. A tiny Hypergon covers 8x10, whereas a huge Aero Ektar won't cover 8x10.

  7. #17
    Rom
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    Hi !

    A very intersting post

    [...] Select a lens with an image circle that is bigger than your measurement.[...]
    My related question is how to calculate the image circle ?

    Thanks for helping

    ++

  8. #18

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    You can't.
    It depends on optical design and mechanical vignetting.
    You have to either ask the manufacturer or try/measure it yourself.

  9. #19
    bvy
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    Quote Originally Posted by Q.G. View Post
    Lenses (being round) 'throw' a round, circular image. Rectangular formats don't use parts of it, but the light in those parts still leaves the rear of the lens.
    It will bounce around, eventually landing on the film too, where it causes a lowering of contrast (at best) or nasty highlights (at worst).
    Interesting. Is there a name for this phenomenon? I'd like to learn/read more about it, and how to control (or temper) it.

  10. #20

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    There is. It's called "flare".

    There are three ways to control it:
    - antireflection coating of lens elements and matt black paint on the inside of the lens barrel and the inside of the camera,
    - baffles in and behind the lens that block as much non-image forming light as possible,
    - the use of a good lens hood, that prevents non-image forming light from entering the lens in the first place.

    The last thing is the only one you can do. And it is very important to indeed do this.

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