Rethinking focal length conventions

Started 7 months ago | Discussions thread
jrtrent Veteran Member • Posts: 6,221
Re: 6%
3

Phil A Martin wrote:

Pixel Pooper wrote:

Phil A Martin wrote:

Pixel Pooper wrote:

Phil A Martin wrote:

Paul Pasco wrote:

My observation going back to the 70’s was that when you put a 50mm or so lens on a DSLR and looked through viewfinder with both eyes open, the size of objects appeared very close to the same

And this is the important point, not the angle of view. With a 43mm lens, the sizes would appear even closer.

This depends on viewfinder magnification. On my 35mm SLR sizes look the same at 52mm, but on my A7III it is 65mm and on my RX100 it never happens because the lens isn't long enough.

Paul Pasco said "through viewfinder with both eyes open, the size of objects appeared very close to the same" and I replied "With a 43mm lens, the sizes would appear even closer". Neither of us said they would appear exactly the same through the viewfinder as with the naked eye.

At 43mm the sizes would not appear closer. With a viewfinder magnification of 1 they will be the same size at 50mm. Most cameras have a viewfinder magnification below 1 so the sizes will appear the same at a focal length longer than 50mm. For them to be the same at 43mm you would need a viewfinder magnification of 1.16 which is not available on any FF camera.

So now you have a better idea of what I can see through the viewfinder of my own camera with my own eyes than I do. How did you get this super power, a radioactive lens maybe?

This conversation is over. It's not going anywhere and I no longer wish to exchange pedantries with you. It's a 2aste of time. Goodbye.

From an article called "Understanding Viewfinders":

Magnification: this refers to how big the viewfinder image appears to be in an absolute sense. Like a batting average, it’s usually expressed as some decimal fraction of one. 1X is the size that things appear to be when you look at them with your eye (a.k.a. “the naked eye”). Now, obviously, magnification also changes when you use different lens focal lengths — telephotos make things look bigger, wide-angles make things look smaller. So camera magnification is specified with a 50mm lens. Less often stated is that the lens must be set at infinity, because magnification also changes slightly depending on how close or far you focus the lens.

Let’s say a camera’s magnification is .75X. What this means is that your camera, with a 50mm lens on it, set at infinity, makes things appear to be three-quarters the size they look to be with your naked eye. .5X means half as big; .9X means nine-tenths as big. https://luminous-landscape.com/understanding-viewfinders/

I've read that 58mm lenses were desired by some because they provided life-size viewing on some cameras. For example, "The 58mm focal length provided 1:1 viewing on the Contax S focusing screen." https://casualphotophile.com/2019/02/13/carl-zeiss-jena-biotar-58mm-f-2-lens-review/

I don't know which SLR's in the 1970's Paul Pasco was thinking of, but my Pentax SP1000 had a .88X viewfinder magnification, and my Contax 139Q was .86X.  The 55mm lens on my Pentax would have been closer to life-size viewing than the 50mm lens on my Contax.

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