What determines neg. size? 6x4.5 and 6x6

Discussion in 'Medium Format Cameras and Accessories' started by hammy, Dec 30, 2006.

  1. hammy

    hammy Member

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    I'm a bit confused on something.

    What determines the negative size/aspect ratio with 120 film? In other words, what determines if it's 6x4.5 or 6x6?
     
  2. Woolliscroft

    Woolliscroft Member

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    The camera.

    David.
     
  3. Dave Miller

    Dave Miller Member

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    The size of the mask in the camera through which the image is formed on the film. It's nothing to do with the film itself.
     
  4. Roger Hicks

    Roger Hicks Member

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    First, all sizes are nominal, and almost invariably, the actual size is smaller than nominal.

    The maximum image width on 120 film is 56-58mm. The image can be any length, but typical choices are 40-44mm (645 = 15-on or 16-on), 56-58mm (6x6 = 12-on, 11-on in some very old cameras), 67-72mm (6x7 = 10-on), 78-80mm (6x8 = 9-on, rare), 80-88mm (6x9 = 8-on, the original 120 format), 110-120mm (6x12 = 6-on) and 170mm (6x17 = 4-on).

    Any camera can be built for any format; some accept different backs or use masks for multiple formats.

    Cheers,

    R. (www.rogerandfrances.com)
     
  5. hammy

    hammy Member

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    Thanks.

    That's what I thought.

    So my Hasselblad 500C, it's 6x6?
     
  6. Roger Hicks

    Roger Hicks Member

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    Usually but 645 backs are available. Measure the gate with a ruler and you'll know. Or count the exposures...

    Cheers,

    R.
     
  7. srs5694

    srs5694 Member

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    Or measure the size of the images on a processed roll of film.
     
  8. Len Robertson

    Len Robertson Member

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    Hasselblad backs are usually referred to by the number of exposures per roll - 12 (look through a hole in the back to advance film to #1 frame) or A12 (auto stop at first frame). Both are 6X6 frame size and take 12 images per roll of 120. There are also 16 and A16 backs for 6X4.5 frame size, and 16 exposures/120 roll. There is an A24 for 24 exposures 6X6 on 220 film (not many 220 films left on the market). The back you probably want to avoid is the 16S which was designed for 4.5X4.5 "Superslides". Finally there is a 70mm 6X6 back which takes many exposures per roll, but the choice of 70mm films is rather limited.
    If you are shopping for an additional back for your 500C, the A12 back seems to be most common on the used market. Myself, I get along fine with the older non-auto 12 backs. This may be the style back you already have with your 500C. They tend to be less expensive than the A12. 16 and A16 backs are much less common on the used market, but there are some available if the 6X4.5 and 16 exposures per roll are important to you.
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    Lens has some part in this too.

    A 70 mm lens for a 35mm camera will not work properly on a 645 camera where 70 mm might be considered normal. Even if the mounts were the same, the image would not be correct due to vignetting among other things.

    PE
     
  10. jstraw

    jstraw Member

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    Lens vignetting could prevent the frame area from being completely exposed but it has no role in determining what that area is.
     
  11. Photo Engineer

    Photo Engineer Subscriber

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    A 70 mm lens for 645 and one for 35mm cover different negative areas evenly at the focal plane due to design, not actual theory involved in optics. It is a matter of economics.

    This also involves the plane of object focus of a lens which is nominally curved and must be designed for the given film size. Again, this is a matter of economics rather than theory. So, a 35mm lens is designed with a smaller area of coverage and a smaler area of focus compared to a similar lens for 645.

    A lens for a large camera can more easily be adapted to a smaller frame camera than the other way around.

    At least, this is a practical rule of thumb I was given when I was learning these things.

    So, it is a matter of practice and econimics vs what is theoretically and really possible given an unlimited budget.

    It can be demonstrated by focusing a scene from two 70 mm lenses on a sheet of paper outside of a camera and observing the circle covered by both lenses on the paper. This is how it was demonstrated to me at one time.

    I'm not an optics person, so I'm only reporting on observation and what I was taught pursuant to other elements of system design.

    PE
     
  12. jstraw

    jstraw Member

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    You're thinking too hard. I don't need to know a thing about lens design to know that it's entirely separate from what determines that one camera is shooting 6x4.5 and another is shooting 6x6. The lens is not in any way part of that equation, if you want to call the size and shape of the mask at the film plane an equation. The masking at the film plane is the only thing that determines the answer to the original question.
     
  13. Photo Engineer

    Photo Engineer Subscriber

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    You are right if it is between 6x6 and 645, but if it is 6x6 and 4x5 or 6x6 and 35mm, then it wont work for reasons I stated.

    I only wanted to make sure that people did not expect to put lenses from widely different camera formats on the wrong camera and expect to get good results.

    PE
     
  14. jstraw

    jstraw Member

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    I only wanted to make sure that the guy understands that this concept that you've introduced; mixing lenses from different formats, has nothing to do with answering his very simple question:


    "What determines the negative size/aspect ratio with 120 film? In other words, what determines if it's 6x4.5 or 6x6?"​
     
  15. Robert Budding

    Robert Budding Member

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    There are also different formats for 135 film. The Olympus Pen cameras are 1/2 frame. And the old Zeiss Tenax is 24x24.