6x7 equivalent focal lengths in 35mm

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.

"...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.

Dredging up and old post:

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.<div>[ATTACH=full]924980[/ATTACH]</div>

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.

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,

Bob

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,

Bob

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?

I use a simple method of thinking, magnification based on the standard normal lens for that format.

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.

So to recreate something shot on an 80mm lens, I'd have to use a 32mm lens (and crop the sides to match)

- 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.