How are the image circles so big on xpan lenses?

Discussion in 'Panoramic Cameras and Accessories' started by cfrye, Sep 14, 2018 at 1:29 AM.

  1. cfrye

    cfrye Member

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    So recently, I've been interested in different approaches to 35mm pano work. Obviously when one goes beyond the 24x36 the image circles of most lenses designed for that format go whack. My question is: how did the designers of xpan lenses enlarge the image circle so much without a significant increase in lens size (from other rf lenses in general)?

    Is it purely smart optical design or is there some other factor that I am missing?
     
  2. nakol

    nakol Member

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    I believe the lens was designed for medium formats.
    And since it does not have to have the shutter within the lens, the lens can be relatively slim.
     
  3. billbretz

    billbretz Member

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    I would think the relative slowness (f4 and 5.6) plus the sometimes necessary center filters are part of the tradeoff.
     
  4. halfaman

    halfaman Member

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    With the lack of prism in the camera you can have the rear element as close as you like to the film plane, that makes that the lens desing can be very compact. Think about the Angulon lenses orginally desing for 6x9 but able to cover 4x5'' stepping down with no movements. They are ridiculously tiny (filter thread M30.5).

    [​IMG]
     
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    cfrye

    cfrye Member

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    I certainly think the lenses were designed for medium format (is xpan technically medium format?), and that the slowness is a tradeoff for larger image circle. I guess I just don't understand the basic principle behind designing lenses specifically for a larger image circle... For example, does a 90mm f4 lens designed for a 24x36 rangefinder have the same image circle size as the xpan 90mm f4??
    If it doesn't, why?
     
  6. Nodda Duma

    Nodda Duma Subscriber

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    It is not difficult, just different optical requirements and so a different starting point (I’m a lens designer).

    From a design standpoint, 35mm camera objectives are one small category in the lens design universe. The 35mm frame is just one image size in a wide range of image sizes (and visible spectrum objective lens just one imaging application amongst many).

    The diameter of the image circle is defined by the diagonal, and is a basic 1st order property established when the design work begins.

    Like the design of an automobile begins with, say, how many passengers will it carry. Not a big deal at all do define it starting out, but a two seat sports car will have a different (yet similar) design path from, say, a bus. This isn’t a perfect analogy, because the two different optics will be more similar, but you get the idea: you won’t be able to bus a bunch of people around in a sports car even if they both have 4 wheels, an engine, door, etc.
     
    Last edited: Sep 14, 2018 at 11:57 AM
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    cfrye

    cfrye Member

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    Very interesting. Any suggestions for reading materials on that general subject that aren't super very incredibly technical?
     
  8. Nodda Duma

    Nodda Duma Subscriber

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    Kingslake “The History of the Photographic Lens”

    Other than that, no. Lol. Optical design is incredibly technical as it’s rooted in physics.
     
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