How do medium format focal lengths correspond?

Discussion in 'Medium Format' started by ron_hughes, Mar 27, 1998.

  1. Background:

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    I have used 35mm SLRs for about 40 years and have just recently bought a secondhand ETRS with a 75mm lens. I gather this corresponds to the standard 50mm lens on a 35mm camera.

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    Questions:

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    How do other medium format lens focal lengths correspond to 35mm ones?
    What is the best focal length for landscape photography?

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    I feel like I'm starting out all over again! Any advice would be welcome. Thanks.
     
  2. Check out http://www.photo.net/photo/lens-table.html which gives comparable lens lengths for various formats and print aspect ratios.
     
  3. There are actually considerable variations and disagreements on this issue! Some references are annoyingly complicated, but the basic rule of thumb for 35 to (say) 6x7 (2-1/4 inches by 2-3/4 inches) is about one-half, and it's fairly easy to extrapolate from there. Thus, a 180 on an RB is roughly the same as a 90 on 35mm film, and a 50 is similar to a 24mm wide angle, etc. Where this intentional oversimplification doesn't hold is in the area of how a lens of a given focal length "sees," which always stays the same. In other words, an 80mm lens on 35mm at any given distance will produce the same image as an 80mm lens on a standard Rolleiflex at the same distance. In the first case, it may be a head and shoulders shot, while in the latter, it might include the whole person and part of the surroundings. But if you cut out a little picture of the head from both, they will look the same, because they were both taken with an 80mm lens, just on different formats (one being larger than the other). So the "roughly half" rule refers to coverage (how much gets in the picture), while the "stays the same" rule refers to how the subject is rendered at the same distance.
     
  4. A standard focal lenth for a given negative size is supposed to be the
    diagonal of the exposed area. A 35mm negative is 24x36mm, which is
    43.5 diagonally. However, only 24x30mm is actually used for an 8x10
    print. So based on that, here are the standard focal lengths for the 4
    film sizes:
    for an 8x10 aspect ratio:
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    35mm (24x30mm useable area) 38mm
    6X4.5cm(43x54mm useable area) 69mm
    6x6cm (45x56mm useable area) 72mm
    6x7cm (54x67mm useable area) 86mm

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    for a 9x16 Pythagorean "Ideal" aspect ratio:
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    35mm (20x36mm useable area) 41mm
    6X4.5cm(32x56mm useable area) 64mm
    6x6cm (32x56mm useable area) 64mm
    6x7cm (38x67mm useable area) 77mm

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    You can do the math from there.
     

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