A question regarding Medium format lenses…

Discussion in 'Medium Format Cameras and Accessories' started by imageWIS, Oct 22, 2005.

  1. imageWIS

    imageWIS Member

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    In a medium format camera with removable backs, does a particular lens have limitations regarding what size film type it can handle? Is there a limit? I.e. if a camera has a 105mm lens attached and a person is shooting with a 6x6 back but then decides to shoot with a 6x9 back, does he have to change lenses?

    How does ALPA solve this problem (since their cameras can accept 645, 6x6, 6x9, etc…)?

    Thanks!

    Jon.
     
  2. Dave Parker

    Dave Parker Inactive

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    Normally the image circle of the MF lens is far larger then the recording size of the back, as I stated earlier today, I have used 35mm lenses on 4x5 gear and it almost covered the whole recording area of the 4x5 format film, normally any lens offered for a particular MF system will cover anysized film back they offer on this type of camera.

    Dave
     
  3. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    View camera lenses generally are not associated with a particular format or camera brand, but part of their spec is the maximum image circle, which dictates the maximum format size, as well as the maximum format size for a particular purpose. For instance, you might need a lens with an extra large image circle for architecture.

    Lenses for the Alpa seem to be Schneider view camera lenses that have been tweaked to give better performance wide open, perhaps at the expense of excess image circle, but they should still cover the maximum format of the camera, or if they do not at the wide end, they would be purchased just as wide lenses to be used with the formats that they do cover, just as lenses would be selected for use with a large format system.

    With modular medium format SLRs that might have the options of different format backs (like 645 on the 6x6 Hasselblad or Bronica), the lenses are dedicated to cover the maximum format size, and the smaller format backs may be provided for convenience in certain situations.
     
  4. glbeas

    glbeas Member

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    If a camera system is designed with removeable backs with a variety of formats you can bet your bottom dollar the designers took that in to consideration when designing the lenses for that system. They will all cover the largest format the camera offers. The Bronica system I have is a good example, each larger system has backs to do the formats of each of the smaller systems. The GS-1 has 6x7, 6x6, and 6x4.5 backs, the SQ has 6x6 and 6x4.5 and the ETR has its native 6x4.5 format and as well theres a 35mm pano back made for all of them. Each system has thier own lenses that can't be used on the others (I think thats not the best idea) that are designed to cover the largest format that camera body will see.
     
  5. imageWIS

    imageWIS Member

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    What is the lens diameter needed for a 6x9 camera?

    Jon.
     
  6. Dave Parker

    Dave Parker Inactive

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    The circle of coverage for a 6x9cm would have to be at least 9cm in diameter to give full coverage. It really has nothing to do with the diameter of the lens, but the diameter of the projected image.

    Dave
     
  7. MattKing

    MattKing Subscriber

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    I wouldn't be surprised if it varies with the lens.

    I have a 150mm f/3.5 lens for my Mamiya 645 that has an internal baffle near the lens mount that appears to be in the same shape as the film format - i.e. a ratio of 6 horizontal to 4.5 vertical. I have never seen any definitive explanation for its presence there, although I expect it is related to controlling flare.

    If you tried to use this on 6 x 9, I wouldn't be surprised if you would have problems with vignetting.
     
  8. Dave Parker

    Dave Parker Inactive

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    Matt,

    I would expect a lens designed for 645 to vignette on a 6x9, that seems to reason, All of my Mamiya lenses have square exits at the mount end of the lens, including my 500mm

    Dave
     
  9. Donald Miller

    Donald Miller Member

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    For your future reference the image circle required for any lens is determined by determining the hypotenuse of the right triangle. The formula for this is H2 equals A2+B2...in the case of a 6X9 camera this would be 36+81 or 117...the square root of 117 is almost 11 cm.
     
  10. Dave Parker

    Dave Parker Inactive

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    Sorry Donald, I posted before I engage brain and looked at the longest dimention of the format and engage typing first!

    Yike, I must be tired.

    Dave
     
  11. MattKing

    MattKing Subscriber

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    Dave,

    That is interesting, because none of my other lenses (45mm f/2.8 C - {77mm filter}, 55mm f/2.8 N, 80mm f/2.8 C and 70 mm f/2.8 C {leaf shutter}) have this baffle.

    I too would have guessed that these 645 lenses would have probably vignetted, I just thought that the baffle might make it even more certain.

    By the way, why do you think the baffle is used?

    Thanks,

    Matt
     
  12. Dave Parker

    Dave Parker Inactive

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    Matt being honest with you I really don't know, but I have seen all of the lenses you mention, with and without the baffles, It may depend on the the age of the lenses, but I also have many manual focus Minolta lenses that I used on my XD-11 that have the baffles..

    Dave
     
  13. MattKing

    MattKing Subscriber

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    Dave,

    Actually, if the circle of coverage is, indeed, a true circle, I think that the circle of coverage would have to be the diagonal of a 6x9cm rectangle, or at least 12.041 cm.

    {its my damned training in physics and math - it goes weeks without being used, and then rears its ugly head at the most surprising moments :D}

    Matt
     
  14. Dave Parker

    Dave Parker Inactive

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    Matt,

    I already posted a follow-up that I screwed up and engaged keyboard before brain.. :D

    Dave
     
  15. MattKing

    MattKing Subscriber

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    My apologies Dave - of course you did!

    In case you missed it, in all humility I must confess, in pointing out the correction, I screwed up my calculation!

    Matt

    {Note to self - if you are going to respond to a post - first check if poster has already clarified or corrected same, especially when poster is known to be both accurate and careful!} :D
     
  16. Dave Parker

    Dave Parker Inactive

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    Don't worry Matt,

    Heck a couple of beers and pizza on Saturday night and I am likly to mess just about anything up..... :D

    Dave
     
  17. jmdavis

    jmdavis Member

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    OK then. New rule. Dave can't grind on Saturday night after Beer and Pizza. :smile:

    The lenses for my RB 67 don't seem to have baffles.

    Mike Davis
     
  18. Dave Parker

    Dave Parker Inactive

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    No problems there Mike, I always try to take Saturday night off to spend with the wife and Puppies, here is a pic of one of the puppies, showing how we all kick back on a Saturday night!

    None of my 67 lenses ever had the baffle either...


    [​IMG]

    :smile:

    Dave
     
  19. Woolliscroft

    Woolliscroft Member

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    Remember, though, that a standard lens for 6 x 4.5 with be a wide angle on larger formats, so you might want to change lens for that reason.

    David.
     
  20. Dan Fromm

    Dan Fromm Member

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    100 mm, Dave. sqrt(57^2 + 82^2). 90 mm is the diagonal of nominal 6x7.

    Cheers,

    Dan
     
  21. Dan Fromm

    Dan Fromm Member

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    Matt, 6x9 is a poor metric approximation to 2.25" x 3.25". There are a few 2x3 roll holders with gates longer than 3.25", e.g., the Suydam, which is 84 mm long. And there are some that are shorter, e.g., the Graflex RH-8. Bur a lens that covers 100 mm, and I mean covers, not illuminates, will put good image in the corners of all of them.

    Cheers,

    Dan