dbrugger25 Loc: Raleigh, NC

I think a 50mm lens on a 35mm camera approximates out normal working field of view that does not include much, or any periferal vision. The brain can concentrate on the details of an object that is prominent in one's field of view that makes it seem larger. I think we also do that with people who interest us.

It's hard to do that with a photo without zooming and/or selective focus. The ability of a lens to focus on something and blur everything else approaches the way our brain concentrates on something of interest but our vision is better at keeping the surroundings in focus. It is our concentration on the subject that acts as the brain's filter.

R.G. Loc: Scotland

Focal length determines depth compression or expansion. The crossover between depth compression and depth expansion happens somewhere in the region of 50mm focal length, but it has been pointed out that observed depth in an image varies depending on how close you are to the image (the photo, screen or whatever).

aflundi Loc: Albuquerque, NM

This seems like a pretty easy experiment for anyone to discover for themselves. Maybe we are each different.

I notice that if I walk into a room, I have a pretty good idea of what goes on in a circle of roughly 40 degrees (~58mm equiv.), but I'm not seeing small details except at the center. I have a monitor about 4 feet from me and if I don't move my eyes and concentrate on the text, it looks to me like I can see very good detail in a circle of about 1/2 inch or about 1-2 degrees (~2000mm equiv.). If I want to look at a picture where I have a fairly acceptable level of detail over the entire picture (kind of like circles-of-confusion decision for depth of field), that seems subjectively to me to be a circle of about 30 degrees (~85-90mm equiv.). Of course, with peripheral vision where I have extremely poor resolution on the edges -- I can just see that there is something bright or dark, or moves is all -- that probably goes out to more than 180 degrees (fisheye).

So like the depth-of-field analogy mentioned, it probably depends on how exactly you want or need to perceive the details.

Luft93 Loc: Finger Lakes, NY

This is the best response to the question. I learned the diagonal approximation in about 1946, have used and taught it for decades.
The essential factor is that distant objects appear at at the actual restive size, not closer or farther away. Be aware of single eye viewing.

Bill Waxman Loc: Friday Harbor, San Juan Island, Washington

To achieve the same relative sense of "being there" requires a zoom lens that will allow the shooter to match the view through the eyepiece with the naked eye. This is easier to do, of course, if you use the right eye to look using the camera and the left to match the view. Field of view is meaningless in this sense since you are focusing on getting a three dimensional view with both eyes with a matching view of the object being photographed. Of course, the overall framing of the photo will not include everything seem peripherally with the naked eye, but...

Try it and see for yourself what I am describing.

Bill Waxman

Fredrick Loc: Former NYC, now San Francisco Bay Area

What the eye sees is about 42mm in a FF 35mm camera.

bwana Loc: Bergen, Alberta, Canada

I find a 50-60mm lens best shows what I see.

bwa

kenArchi Loc: Seal Beach, CA

I opened both my eyes, one through the view finder and the other not.
I turned the zoom until the size of the moon through the view finder matched the naked eye view size of the moon.
The zoom lens reading was at about 70mm.

PhotogHobbyist Loc: Bradford, PA

The two human eyes, working in tandem, provide a FOV of approximately 150° to 170°. However our brains provide us with concentration in about the middle of our FOV. Getting that is the area of concentration of a lens, being somewhere in the range of 40mm to 60mm I would guess. There seems to be some distortion of the edges of a photograph taken with 35mm or shorter lenses. The human eye does not distort, probably due to the curvature of the lens and the curvature of the retina. Perhaps if cameras had curved sensors the 18 mm lens would provide a more true view equal to the human eye. Distance from lens to sensor may be the key to a non-distorted view.

Bill_de Loc: US

For three semesters in college, at two different schools and two different professors, 43mm was considered the lens that related to our normal vision. At the same time 50mm lenses were considered normal lenses on 35mm cameras. I took their word for it and never gave it much thought for almost 50 years, until today.

I think it comes from this:

For 35mm film (24mm by 36mm), the diagonal measurement is 43.27mm.

http://www.panoramafactory.com/equiv35/equiv35.html#:~:text=For%2035mm%20film%20(24mm%20by,considered%20a%20%22normal%22%20lens.

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David in Dallas Loc: Dallas, Texas, USA

The discussion has been very interesting, but I consider it moot. Use the lens and focal length that is appropriate for the result you desire. My D7100 (DX) wears an 18-200mm zoom all the time, and I use all of its capabilities when I take photos. Most scenics are at 18mm (or even in a panorama) unless I'm concentrating on some element in view. For flowers I usually use 200mm at the closest focus I can get (approximates a macro lens). I don't worry about what focal length is "normal" or "standard". Nor should anyone, IMO.

reverand

Since the eye keeps moving, it's hard to say what its "field of vision" actually is, simply because the field keeps changing. What you're looking for, I think, is a definition of a "normal" lens, and, as you say, 50mm has long been considered "normal." However, in my experience, different photographers have different ideas of what looks normal. Ansel Adams seemed to prefer lenses in the supposedly normal range, or even slightly longer, although for a 4 x 5, the "normal" lens is considered to be 165mm, which is roughly the size of the diagonal (for 35mm, the actual diagonal would be 43mm).

To me, 35mm looks normal for a 35mm camera, and that's what I use for the majority of my work. However, that's only me.

Longshadow Loc: Audubon, PA, United States

FOV v. Distance to Subject, both relative to the eye.
Never the twain shall meet in a camera lens.

To replicate my eyesight in an image, I'll go with distance to subject being relatively the same.

MJPerini

There are many answers to the posed question, but we should start with three things:
--Cameras see differently than people, --- People see differently from each other,
-- and Human vision 'sees' simultaneously overlapping angles of view in progressively greater detail.
Human vision is quite miraculous. We have that wide peripheral vision with low detail to keep us aware of our surroundings. Then an area of general sharp awareness (the 35-50mm FF type view) and then our head & shoulders portrait view where we have even more detail.
The old 'Format diagonal' is the generally accepted "Normal" and approximates the middle if the three mentioned above.
In the case of FF the Diagonal is about 43mm. Kodak used to make a 44mm Ektar for some of their cameras.
By that standard, 50 mm is a bit long--- the same amount long as 35mm is short which explains why people are divided in their preferences. There have also been many 55 & 58mm "normal lenses manufactured as well as some 40mm lenses that people have loved. (I think Pentax still makes a 43)
None of them are right, and none of them are wrong, it is truly a matter of preference.
Telescopes are sort of a special case, you can mathematically figure out the size of the Moon image you want on the film and construct that. The same telescope can give different sized images depending on weather you use Prime Focus, a focal reducer or expander (a Barlow lens) or an Occular projection arrangement.
If you are Viewing through a Telescope, you are using the equivalent of ocular projection, because the Telescope Eyepiece selected takes the prime focus image and enlarges it by some factor. There is no equivalent of that in a camera--the 'Film/sensor' sees only the prime image.
To be sure the longer the focal length the larger the image of the moon will be. A Teleconverter is the equivalent of a Barlow lens in a Telescope. (it just approximates a longer objective lens)
I hope this helps

rook2c4 Loc: Philadelphia, PA USA

Are you referring to the view of one eye (with other eye closed) or both eyes together?