6x7 equivalent focal lengths in 35mm

Discussion in 'Medium Format' started by alan_southard, Sep 2, 2008.

  1. I have a Horseman 980 with a 6x7 rollback and a 105mm lens. I would like to use it for landscapes and
    macro/product photography. So, what does my 105mm approximately compare to in 35mm format? What focal
    lengths do I need for the 6x7 to approximate the look of 35mm wide angle and 105mm telephoto in 35mm format?
    Is that enough 35's and 105's for ya?
     
  2. Starting with 6x7cm format divide by 2 to get the 24x36mm format equivalent.
     
  3. So my 105mm on the Horseman is my "normal lens" at what would be approximately 52mm on my SLR?
     
  4. It's like 55mm in equivalent, aproximately. Most lenses for medium and small but also large formats are not exactly of focal length specified, say 105mm can be any from 97mm to 112mm in reality. The tolerance by top brands is 5 -7%.
     
  5. Here's a handy memory jog, not sure where I got it from (either my calculator and pencil or 'swiped'). It's not 100% precise, but very close. My 2 cents. Jim M.
    00Qinx-68891684.jpg
     
  6. Very handy table there. I've just purchased a Mamiya M645J with the 80mm lens and was wondering what other lengths might be useful.
     
  7. Alan, this calculator is the most accurate way of comparing focal lengths especially if you want to compare horizontal angles of view. http://www.mat.uc.pt/~rps/photos/angles.html
     
  8. The way I do it is to calculate the diagonal of the film frame (remember Pythagorean theorem? :) ) and compare
    it with the diagonal of 35mm film frame to get the focal length factor. So say for 6x7 (which is something like
    56x68mm actually):

    6x7 diagonal = square root of (56 * 56 + 68 * 68) = 88.09

    35mm diagonal = square root of (24 * 24 + 36 * 36) = 43.27

    thus the focal length factor is 88.09/43.27 = 2.04 (just like Ellis said + my two (per)cents). 35mm in 6x7 would
    be about 70mm in 6x7. The caveat is that 70mm will still have the shallow depth of field just like 70mm mounted
    on 35mm camera so the bigger format you should the tougher is to get everything in focus; on the other hand, if
    you like selective focus, you'll be happy with 100mm being your normal focal length.
     
  9. Thanks for all the help with this. The calculator and table are very helpful.
     
  10. Diagonal fields of view, which are the normal reference, are not the most valid comparisons in your case, as the aspect ratios (height to
    width ratio) of the two formats are quite different. 35mm format corresponds really to a 6x9 medium format. Better to use
    in this case the horizontal rather than the diagonal field of view, whereby the base of 36mm of the 35 mm frame is about one-half of that of
    the 6 x 7 (70mm, but actually a bit less than 70mm, as 70mm is the theoretical frame width and not the practical one measured at the
    camera's film plane).

    Thus, a 35 mm semi-wide angle for 35 mm format should be at most 70mm, prefereably slightly less (or 65mm) in 6x7, as opposed to
    75 mm mentioned in the above table. The other numbers in the table above are somewhat better fits.
     
  11. It's difficult since the aspect ratio of the format are different.

    I use a schneider 110mm with 6x7 and it *feels* to be about 55mm equiv. 90mm feels wider than 50mm.
     
  12. Excellent points about depth of field with 6x7 format. Consider the 35mm camera using 85mm f/1.8 for subject isolation in portraits, the 6x7 portrait lens is often a 150mm f/4. Note that Bronica GS-1 was built to be a lighter 6x7 than Pentax and Mamiya. All lenses are leaf with maximum speed of 1/500 and the lenses are slower f stop which keeps the
    lenses lighter and smaller. Fastest lenses are 80mm f/3.5 and 100mm f/3.5. The 150mm is equivalent to 75mm and the 200mm is equivalent to 100mm neither is particularly close focusing thus an 18mm extension tube is used for close headshots.
     
  13. Wow, this is an old thread.

    To me, when comparing focal lengths the primary thing that matters is the equivalent angle of view in the long dimension. At least with the way I photograph, it's the dimension that almost exclusively dictates how I'm framing whether I'm shooting in a horizontal or vertical aspect ratio.

    To that end, in 6x7 I will interchangeably use either a 90mm or 127mm as my "standard" focal length. 90mm is a bit wider than 50mm(about 45mm or so if I recall), while a 127mm is roughly 58mm. On an RB67, as much as an oxymoron as this may be, I prefer the 127mm as a "walk around." Even though I find it a bit constraining(granted I've also used 55s and 58s in 35mm in the same role), weight considerations ultimately win out and my pre-C 127mm is probably half the weight of my K/L 90mm.

    Since lens weight was brought up, it's also worth remembering that RB/RZ lenses are heavier out of necessity than an otherwise 100% comparable lens for a GS-1, Pentax 67, or even Mamiya 7. The reason for that is that the RB/RZ lenses have to cover 7x7 at a minimum, while the others only have to cover 6x7.
     
  14. Me too. I use to consider first the long side of the format to make comparisons. Then, I imagine the short side given the aspect ratio.
     
  15. "To me, when comparing focal lengths the primary thing that matters is the equivalent angle of view in the long dimension."

    "Me too. I use to consider first the long side of the format to make comparisons."

    Thank you both, guys!
    Not too long ago I was berated for suggesting that using the format diagonal was an absolutely ridiculous way to compare focal lengths. After all, who tips their camera at a jaunty angle to take in more subject width?

    Also, if you compare "standard" lenses across different formats and aspect ratios, you'll find a close match in their long-side angle of view. Not so much in their diagonal AOV.
     
  16. The only time comparing diagonals makes sense-at least to me-is when you have the same aspect ratio. Comparing them on APS-C DSLRs to 35mm or 4x5 and 8x10 would be examples of that.

    Even at that, though, the horizontal dimension(or the vertical dimension) works just as well. i.e. a 300mm lens on 8x10 covers the same as a 150mm on 4x5.
     
  17. Jim Momary's table is as good as any I've seen. I'm normally a stickler for details, but in the case of equivalence between formats with different aspect ratios, close is good enough. the best lens is the one which suits your needs for composition, working distance, etc. To argue whether horizontal, vertical or diagonal field of view is better is simply straining gnats.

    * that expression comes from my grandmother, who canned a lot of fruit. I suspect the gnats got through the strainer, despite your best efforts.
     
  18. "...but in the case of equivalence between formats with different aspect ratios, close is good enough."

    Very true! There's little point working out that you need a 43mm lens if nobody makes one in your camera fitting.

    Having said that, there's also not much point in taking the diagonal or short side of a format like 6x17 as any sort of comparator reference. Or of using the diagonal of 6x6 either.

    Where it does matter is when space is limited. For example; I know off the top of my head that a 17mm lens on 24x36mm has a horizontal AOV of just over 90 degrees, and that if I back the camera into a corner I can take in almost all of a rectangular room. I have almost no idea what the eqivalent lens is on other formats, so I need to do the maths based on the long side dimensions. The diagonal or short side of the frame really don't interest me in this case.
     
    Last edited: Jun 6, 2017
  19. The diagonal dimension is traditionally close to what is considered a "normal" lens for a particular format. In practice, that is rounded off to 50 mm, 80 mm and 90 mm for 35 mm, 6x6 and 6x7 respectively. Even that is a loose definition, because for many, 35 mm is the lens they "normally" use for 35 mm film, 75 mm and 105 mm respectively.

    Part of using a camera is learning to "speak" its language, which includes using the controls without thinking and choosing a lens. The reasoning behind equivalency of lenses for different formats is because most of the last two generations of photographers have grown up with 35 mm film, and intuitively "think" in focal lengths related to that format. After using a medium format camera on a regular basis, you no longer thing of equivalency. You look at a subject and choose the appropriate lens for its own sake, not what you might have selected for an SLR. You also tend to compose to make use the the fatter aspect ration afforded by medium format, even square format, compared to the skinny 3;2 35 mm frame. Actually the same phenomena accompanied regular use of a unique camera like the old "Veriwide" I used in my days at a newspaper.

    The only medium format camera I used at that time was a Rolleiflex with a 75 mm lens. Equivalency is moot when you only have one lens at your disposal. The "tough" choice was whether to use a 35, 50 or 90 with my Leica, or 90 or 135 with a Speed Graphic. More recently in windy, dusty Iceland, I was reluctant to change lenses outside the protection of the car. An early decision was made, "Is this a 16-35, 24-70 or 70-200 moment?" I kinda' gave up on swapping primes in these circumstances. Waking about in the city (Reykjavik) with streets barely wide enough for a car with rear view mirrors, the choice was easier - 25 mm. I have never considered medium format a "walking" type of camera.
     

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