Focal Length Help

Discussion in 'Large Format Cameras and Accessories' started by maxbloom, Nov 8, 2007.

  1. maxbloom

    maxbloom Member

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    So I took an 80mm Rodenstock Heligon off of a Graflex XL and mounted it onto a recessed lens board for my 4x5 monorail. For anyone not familiar with the XL, this lens was built for 6x9 (2.25 x 3.25). Wider than f.11 or so I start noticeably losing full coverage. I'm having a total brain fart tonight. Can anyone please tell me how to figure out (or just tell me) what the effective focal length of this lens is on my 4x5?

    Thanks.
     
  2. Ole

    Ole Moderator Staff Member Moderator

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    The effective focal length is 80mm, on any camera and film size.

    Since there are so many different film sizes in LF it is far easier to think in terms of angle of view, and forget everything about focal length "conversion".
     
  3. maxbloom

    maxbloom Member

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    Alright, but you know what I'm after. I know the lens is still an 80mm lens, no matter what camera it's on. I'm asking what focal length 4x5 lens would yield the same angle of view...
     
  4. PHOTOTONE

    PHOTOTONE Member

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    There are 80mm lenses that will cover 4x5, just not the one you have. But..you want the same angle of view on 4x5 that the 80mm lens gives on roll film on the Graflex XL?

    I would say a lens in the 135-150mm focal length should be about right...but make sure it is designed to cover 4x5.
     
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  5. maxbloom

    maxbloom Member

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    Am I just being really stupid? Is it just an 80mm lens no matter what? I feel for some reason like the field of view of this lens on my 4x5 is wider than the field of view of an 80mm lens built specifically to cover 4x5.
     
  6. Ole

    Ole Moderator Staff Member Moderator

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    A 80mm Super-Symmar XL will give the same angle of view on the 4x5" as the 80mm you have, but without the vignetting. At the opposite end of the price range, so would a 3 1/4" WA Rectilinear (which is what I use in that focal length).

    The field of view would be exactly the same - believe me, I have tried about 20 different 150mm lenses on all film sizes from 9x12cm to 24x30cm, and they all have the same angle of view to within a 1% tolerance!
     
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  7. maxbloom

    maxbloom Member

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    I think perhaps my brain is just not working today.

    And do ordinary 80mm 4x5 lenses typically require recessed boards?
     
  8. Ole

    Ole Moderator Staff Member Moderator

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    That would depend on the camera, not the focal length of the lens. None of my cameras need a recessed board to focus a 80mm lens at infinity, but one I used to have needed it from about 100mm and down.
     
  9. bdial

    bdial Subscriber

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    To expand on Ole's comment a little bit, it depends on how much you can compress the bellows. Several camera makers offer "bag" bellows that don't have accordian folds for working with short focal length lenses.
     
  10. maxbloom

    maxbloom Member

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    Well this is on an orbit. It's not bellows compression, but the fact that the standards collide before I hit infinity.