6x7 equivalent focal lengths in 35mm

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

  1. I agree with this to a large extent.

    My first adventures into MF were burning up a LOT of film in either a Rolleiflex or Rolleicord(I know I went through at least two 20 roll boxes of Provia along with who knows how much Velvia, Tri-X, and some other sldie and color negative thrown in along the way). I have a 75mm on both cameras(I was low budget back in the day, so had 3.5 Tessar/Xenars) and worked only with it. I still managed some great photos, or maybe at least passable ones :)

    When I got my first job, I decided it was time to "graduate" to an SLR but bought my Bronica SQ-a initially with only an 80mm and used it that way for a long time. The most exciting thing to me was that I had a lens that was a half stop faster. In fact, that's still the only lens I have for it, although I'm eyeing a 40mm. I have other systems where I have wider and longer lenses.

    Even though I have a TON of 35mm primes, I tend to have a "3 lens maximum" rule when I go out. My usual kit is a 20mm 2.8, 50mm 1.4, and 135mm f/2. Depending on specific situations, the 20mm sometimes loses out in favor of the 24mm f/2, and I might bump the 135mm to a 200mm 2.8 or if I anticipate macro work might drop down to the 100mm Macro. Of course, if I'm anticipating being close to the car the list might expand, and if I trek very far or have a specific goal in mind I might drop down to two or even a single prime.

    My original serious interest in photography arose from a trip to France in high school. I bought a Canon A-1 and a couple of lenses(mostly off brand, since I didn't know/appreciate how cheap and how much better Canon primes were vs. 80s 3rd party lenses), and hauled them all over with me. I had pretty much everything from 21mm to 200mm covered. After a half a day, most of the stuff stayed in the hotel room. I spent the rest of the trip with the A-1, a 50mm 1.8 hanging around my neck, and a few rolls of film stuffed in my pockets. I didn't find it particularly limiting, and it forced me to work with what I had.
  2. I use this picture to show the difference between different format.
    For me as mostly shoot landscape now, it feels natural to think in horizontal angle.
    If I have equivalent lenses for "all" format, then it is just the amount of sky that varies between the different format.

    And the table Jim did show gives a good enough value for equivalent lenses.

    But, as the picture indicates: I never shoot 6X7..

    Last edited: Jun 7, 2017
  3. "The diagonal dimension is traditionally close to what is considered a "normal" lens for a particular format."

    - I think the key word there is "traditionally", as in back in the C19th century when cameras mainly came in 10x8, whole, half or quarter plate. Formats which all have approximately the same ratio.

    The diagonal is also useful to lens designers and users of large format cameras to decide if the image circle of a lens will cover a given sheet of film. Other than that, it really is a totally silly way to compare lenses across formats with different ratios.
  4. The diagonal of 4x5 is 6.3" or 162mm. This is indeed an important number to keep in mind when lens shopping, but realistically I'm looking for lenses that have image circles substantially larger than this(it's an important enough value that it's usually prominent in the lens specs).

    As an example, the well regarded Nikkor-W 150mm f/5.6 is listed with an infinity image circle of 174mm wide open and 210mm at f/22. Since LF lenses aren't used wide open all that often, the latter is a more important number.

    In any case, that guides me on how much I'm going to be able to get out of the lens in terms of movement. Also, within reason, bigger is better as the quality typically starts to degrade at the edges of the circle so ideally I want something that gives me "room to spare" on the movements.

    All of that is irrelevant on your typical MF camera, though, as we can safely assume that any quality maker has provided more than enough image circle to fully cover the frame and to minimize wide-open vignetting as much as realistically possible.

    On the subject of the long angle, I'll also mention that even in portraiture I'd consider it more important than the short angle at least in the 645-6x9 range. Peoples' faces are longer than wider, so if taking a head shot you'll usually be fine on the short angle at the 2:3 aspect ratio or less. This is even more true when you start including more of the person's body since, again, most people are taller than they are wide.
  5. I don't recall ever consulting an equivalency table when shooting a portrait. Regardless of the film or format, I make it a point to stay at least 5 feet from the subject, if I want the subject to look best rather than satisfy some artistic whim. For that matter, I don't consider equivalency when shooting landscapes or anything else either. I pick a lens that works.

    The only time equivalency is an issue is when you're buying equipment with which you're functionally unfamiliar. Even then, you're more likely to consult others who have real experience, including via the internet. The field of view is proportional to whichever dimension you use to compare two lenses - focal length, diagonal, short side or long side. Much ado about NOTHING.

    In my experience, not many lenses have an image circle that actually covers the format when wide open. That's why we consider "vignetting". It's a matter of degree rather than kind.
    Last edited: Jun 8, 2017
  6. I can see the arguments for considering the long side only and dispensing with diagonal or short side considerations; it makes sense when shooting a portrait, building, or interior.

    However, there are circumstances where "long side thinking" doesn't help. 645 and 6x6 have the same long side dimension - 56 mm. As does 35mm full frame digital and some old square MF digital backs - 36 mm. But I select cameras and lenses for these formats quite differently. I consider the area, more than the width or height. Shooting landscapes, skies, or astrophotography, much impact comes from the overall spaciousness. Thus, although I mount the same set of Mamiya 645 lenses on my Kodak DCS645M and EOS 5DII, both with 36mm long dimension, if I were to select 55mm for the digital back, I'd tend to select 45mm for the Canon to achieve equivalent effect; it would seem cramped otherwise.
  7. "...much impact comes from the overall spaciousness."
    - How do you define or quantify spaciousness?
    By area? Surely that's just dependent on the final print or viewing size?

    10"x8", 9"x9", or 7.3"x11" all have the same area. So which is more "spacious"?
    And doesn't the concept of cropping belong in there somewhere?
    After all, a 6x17cm pano is just a sheet of 5"x7" that's been severely cropped. Or likewise a full-frame digital image.
  8. Double post. Apologies!
  9. Dredging up and old post:
    I think the big point is, it depends on your end goal. To get a generally similar feel? Or to recreate something? Irrelevant if the aspect ratios are the same, but important if they're not. For example, I'd like to try to recreate some old photos that my dad took in 6x6. If I use that chart, I'll get about the same visual information from side to side, but the top and bottom will be cut off due to the wider aspect ratio of 35mm. So to recreate something shot on an 80mm lens, I'd have to use a 32mm lens (and crop the sides to match) rather than a 48mm lens (and have the top and bottom cropped for me). The inverse would be true if you were trying to recreate a 35mm shot using 6x6.
    Gary Naka likes this.
  10. How about the equivalent focal length (or is "crop factor" the correct term?) if mounting a 6x7 lens to a 35mm?

    I have a beautiful old Carl Zeiss Jena 180mm f/2.8 with a Praktica mount, as well as an interesting Arsat 30mm f/3.5 fisheye, that I bought for an old Kiev 60 I have. I've noticed Praktica-to-Nikon F Ai adapters on the big auction site for less than twenty bucks. Do you think it's worth buying the adapter to try these lenses on my D750 or Nikon film bodies?

    Stay sharp,
  11. A 6x7 180mm lens will still be a 180mm lens on a FX or 35mm camera.
    If you have a zoom that covers 180mm, set the zoom to 180mm, and that is what you will get with the Zeiss 180. A 3.6x tele.

    But there is the question of, will the older lenses stand up to the high resolution sensors?
  12. I use a simple method of thinking, magnification based on the standard normal lens for that format.
    A 105 on a 35mm/FF camera is about 2.1x the 50mm normal lens.
    A 150 on a 6x6 camera is about 1.9x the 80mm normal lens.​
    So both lenses are about 2x magnification.

    This does not account for V/H format difference between formats, but it is a quick easy way for me to get close, without the confusion of "equivalency."
    Besides, for some cameras, you do not have much choice. You get what is available and in your price range.
    Example, I wanted the Hasselblad 180, but had to settle for the more available and cheaper/affordable 150.​
  13. - You're assuming that '6x6cm' negatives are actually 60mm square, which they're not. They'll be 56mm square at most.

    The largest equivalent area you can get from a 35mm frame is 24mm square, so by simple division the focal length multiplier/divider is 56/24 = 7/3 = 2.333.

    An 80mm lens equivalent would therefore be 34.3mm on 35mm, and a 75mm lens would be approximately 32mm.

    The APS-C equivalent focal lengths would be 22.9 and 21.4mm.
    lukpac likes this.

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