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  1. #1
    duparis00's Avatar
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    6x9 Crop Factor?

    Hey All,

    So I'm getting a Rollex 6x9 back for my Linhof, so I can use 120/220 film on the 4x5. I'm just trying to figure out what angle of view I'd be getting in 35mm terms, if I put on say a 90mm lens? On the 4x5 that's a good wide angle, on a 645 it's like a 50mm equivalent, but what does it translate on a 6x9 frame? Likewise I have a 180mm and wondering how I should calculate that as well.

  2. #2

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    The "normal" lens on 6x9 is in the 100mm-110mm range.

    Because of the 6x9 format, you capture a lot of a scene within that frame.

    I guess the best way would be to compare photos taken with a 35mm, 6x6 and 6x9.

    I feel comfortable saying that 6x9 provides a much wider view than 35mm. The field of view feels like 28mm but without getting that wide-angle "feel" from your photos.
    Last edited by elekm; 08-03-2014 at 10:45 AM. Click to view previous post history.

  3. #3

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    Quote Originally Posted by duparis00 View Post
    Hey All,

    So I'm getting a Rollex 6x9 back for my Linhof, so I can use 120/220 film on the 4x5. I'm just trying to figure out what angle of view I'd be getting in 35mm terms, if I put on say a 90mm lens? On the 4x5 that's a good wide angle, on a 645 it's like a 50mm equivalent, but what does it translate on a 6x9 frame? Likewise I have a 180mm and wondering how I should calculate that as well.
    Nominal 6x9's (2.25" x 3.25", 6x9 is a lousy metric approximation) normal focal length (diagonal of the frame) is 100 mm. 24x36's normal focal length is 43 mm. A 90 mm lens on 2x3 (short way of referring to 2 1/4 x 3 1/4) sees what a 39 mm lens would see on 24x36. Shortish normal lens, really. Do the arithmetic yourself for y'r 180 (hint, 180 = 2 * 90).

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  5. #5
    duparis00's Avatar
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    Wow, thanks for the great info guys, it's exactly what I was looking for! That lens chart is gold, thanks Dan!

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    Calculating "normal" FL (traditional) formula: square root of image length squared plus image width squared...

    (6x9cm)
    56^2 + 84^2 = 10192
    sqrt of 10192 = 101mm (normal for 6x9cm according this old formula)

    90(your lens' FL) / 101(normal lens' FL) = .89

    normal FL for 135 format is 43mm
    .89 x 43 = 38mm equivalent on a 135 format camera... just shy of normal

    Many consider the old traditional formula flawed preferring to use the long edge of the image area for calculation but I don't know a formula for that. I'd "guess" multiplying the long edge by 1.2x is pretty close.
    Last edited by Old-N-Feeble; 08-03-2014 at 01:23 PM. Click to view previous post history.

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    Um, er, ah, 2x3 and 24x36 have the same aspect ratio so comparing the formats' long, or for that matter their short, side as a basis of comparison is equivalent to using the diagonal. The diagonal is the conventional basis but as we've seen some people don't follow the convention.

    O-N-F, all dimensions of 2x3 are approximately 2 1/3 times the equivalent dimensions of 24x36. I don't know where you got your 1.2 times.

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    Ascertaining the aspect ratio and the 35mm equivalent in lens is all fine and dandy, but you need to bear in mind when you compose on that large 4x5 ground glass that you are not using the entire image. You are already cropping down to 6x9cm, and it makes zero difference what ever lens you decide on for standard, the image you capture is pre-cropped. to fit the back. I hope you have some guide lines to figure where the 6x9 is going to be when you trip the shutter. Honestly, I seriously considered a 6x9 back for my 4x5, but came to the realization that is was a waste of time and film. If you really want that size negative, get a dedicated camera for it. Now, if you were talking 6x12, that might be another story.
    Rick A
    Argentum aevum

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    Quote Originally Posted by Dan Fromm View Post
    Um, er, ah, 2x3 and 24x36 have the same aspect ratio so comparing the formats' long, or for that matter their short, side as a basis of comparison is equivalent to using the diagonal. The diagonal is the conventional basis but as we've seen some people don't follow the convention.

    O-N-F, all dimensions of 2x3 are approximately 2 1/3 times the equivalent dimensions of 24x36. I don't know where you got your 1.2 times.
    Of course that's true, Dan. You're correct as usual. I just added that tidbit of information in case the OP ever decided to shoot 6x6cm, 6x7cm or 6x12cm. I "guessed" at the 1.2x factor for choosing a normal lens based on long edge...

    6x6cm..... 56 x 1.2 = 67mm

    6x7cm..... 70 x 1.2 = 84mm

    6x9cm..... 84 x 1.2 = 101mm

    6x12cm... 112 x 1.2 = 134mm

    I'd "guess" that's fairly close although 1.22x or 1.25x might be closer. However, I'm sure there are better calculations. I just don't know of any.

    Using 1.25x instead...

    6x6cm..... 70mm

    6x7cm..... 88mm

    6x9cm..... 105mm

    6x12cm... 140mm

    Yeah, those seem more reasonable. So my NEW "guess" is 1.25x to calculate normal FL based on the long edge of the image.
    Last edited by Old-N-Feeble; 08-03-2014 at 03:15 PM. Click to view previous post history.

  10. #10

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    O-N-F, what does your 1.2 or 1.22 or 1.25 have to do with the OP's question? You've lost me completely.

    Rick, I use a 4x5 standard and focusing panel to shoot 6x12, have reluctantly decided to park my 2x3 gear and use my 6x12 rig for that format with, of course, a 2x3 roll holder that fits it. By an odd coincidence the 4x5 focusing panel is marked for smaller formats so framing for them with it isn't much of a problem. I just have to pay attention to the frame lines. As it happens, the 2x3 roll holder I got to use with my 6x12 rig has a gate that's offset from the camera's optical axis. Putting additional marks for framing with it wasn't hard.

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