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Thread: Why are lenses never measured in square format ?

  1. #1
    Alex Timmermans
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    Why are lenses never measured in square format ?

    I am just wondering
    Why are lenses never mesured in quare formats.
    We always talk about lenses suitable for 4 x 5, 8 x 10, etc.
    But they actually cover 5 x 5 or 10 x 10.


    Alex
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  2. #2
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Why are lenses never measured in square format ?

    First...
    Because they're defined in terms of common film formats... 4x5 is... 5x5 is not.

    Second...
    A lens that covers 4x5 might not cover 5x5, since the diagonal of 5x5 is larger than that of 4x5.

    Lenses for some medium format cameras, particularly Hasselblad, are measured for square format (6x6).

    - Leigh
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  3. #3

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    Re: Why are lenses never measured in square format ?

    Quote Originally Posted by alex from holland View Post
    I am just wondering
    Why are lenses never mesured in quare formats.
    We always talk about lenses suitable for 4 x 5, 8 x 10, etc.
    But they actually cover 5 x 5 or 10 x 10.


    Alex

    Actually, lens cover a circle, not a square format.

    Sandy
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  4. #4

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    Re: Why are lenses never measured in square format ?

    Quote Originally Posted by sanking View Post
    Actually, lens cover a circle, not a square format.

    Sandy
    snap!

  5. #5
    Vaughn's Avatar
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    Re: Why are lenses never measured in square format ?

    Just for fun, I drew it out. A circle for 5x5 is about 7" and for 4x5 is about 6 3/8" in diameter.

    Film dimensions are a bit smaller than stated size, but close enough.

  6. #6
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Why are lenses never measured in square format ?

    Quote Originally Posted by Vaughn View Post
    Just for fun, I drew it out. A circle for 5x5 is about 7" and for 4x5 is about 6 3/8" in diameter.
    How about basic trigonometry?

    Diagonal = sqrt( a^2 + b^2 )

    5^2 + 5^2 = 25 + 25 = 50; sqrt( 50 ) = 7.071

    4^2 + 5^2 = 16 + 25 = 41; sqrt( 41 ) = 6.403

    - Leigh
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  7. #7
    Vaughn's Avatar
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    Re: Why are lenses never measured in square format ?

    Because "sqrt" looks too much like "squirt" and sounds a bit rude (like Giclee).

    Also I was wrapping my head around the image circle needed for 4x5 rotated for both horizontal and vertical orientation and the visual helped. Of course it is the same, but seeing it helped.

    vaughn

  8. #8
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Why are lenses never measured in square format ?

    Hi Vaughn,

    I wasn't being critical. I was just playing, and pointing out how close your measurements actually were.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  9. #9
    Vaughn's Avatar
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    Re: Why are lenses never measured in square format ?

    All in fun...

    Plus I was up at the darkroom until 4am or so and got to bed at 5am -- then up at 9am. My brain won't do "higher" math right now. LOL!

    Vaughn

  10. #10

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    Re: Why are lenses never measured in square format ?

    They used to be offered with coverage defined by format. Rectangles, usually. Look at the older B&L catalogs on www.cameraeccentric.com

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