How can you see what I saw?

November 1, 2009 5:40 PM

In 35 mm terms, how wide angle are our eyes?

Understanding that we have our main vision, what we're actually focusing on, and our peripheral vision, what we can sort of see, what're the answers to this? For example, can we focus the equivalent of a 22mm lens on a fullframe 35mm? I understand that our eyes and brain are much more complex than a lens; I'm more interested in the physical frame in terms of what lens would most closely replicate natural vision.

posted by history is a weapon to science & nature (20 comments total)

A 50mm lens is the closest to human vision.
posted by meadowlark lime at 5:47 PM on November 1

The conventional wisdom is that a 50mm lens (on a 35mm camera) is approximately the same as what we see with the unaided eye, and that's why cameras generally used to come with a 50mm "kit lens".
posted by xil at 5:48 PM on November 1 [1 favorite has favorites]

http://www.cambridgeincolour.com/forums/thread106.htm#post416

More: http://www.google.com/search?hl=en&q=focal length human eyes 50mm
 
posted by querty at 5:50 PM on November 1

With normal eyesight, our peripheral vision approaches 180 degrees. Camera lenses don't usually approach that without the distortion typical of, e.g., a fish-eye lens.
posted by TruncatedTiller at 5:52 PM on November 1

Apparently our field of vision, left to right, is about 200 degrees. A 22mm lens on a 35mm camera gets you an angle of view of about 185 degrees.

However, yes a 50mm "normal" lens is going to match the human eye more closely in terms of perspective and magnification.
posted by reegmo at 5:53 PM on November 1

Just to add to the above - there's field of vision and perspective. Field of vision = how wide you can see. Perspective is how "screwed" things look.

This makes replicating "human" vision in photography pretty difficult - the same thing that you see if you look around you could really only be captured with a 50mm or so lens, but way, way, far back. If you ever see films made, or studio photography, you'll note that the photographer is further from the subject than you would "intuitively" think.

I find that's also a common learning curve for budding photographers - zoom out and step back for a more "natural" shot. (that also has its own set of drawbacks, but that's a whole separate comment).
posted by olya at 5:56 PM on November 1

yes - a 50mm lens is going to give you the field of vision. HOWEVER, if you put this lens on your DSLR camera, you might not get a true 50mm, due to something called the crop factor. You can google it or read more about it here Crop Factor Explained

So on my canon DSLR, my 50mm lens is actually giving me the equivalent of 80mm.
posted by smalls at 5:57 PM on November 1

Pardon my ignorance, but would using an extra-wide panorama-style film and a 50mm lens be closer?
posted by krilli at 5:58 PM on November 1

reegmo, I agree that the human left to right field of view can be over 180 degrees (at least for movement and light recognition), but a 22mm lense is nowhere close to that wide. In fact it is closer to 80 degrees wide. You realistically need a 16mm or wider lens to be able to stand in the corner of a room and have both walls on either side of you visible stretching away from you in the shot.

That is getting pretty close to fish-eye territory, which I believe is the only way to get a view angle wider than about 120 degrees.
posted by meinvt at 6:14 PM on November 1

50mm is generally considered "normal perspective" on a 35mm negative. However, this is not a well defined concept because human vision is not so simple. We have significant perception in the periphery that functions differently than the vision we have in the center of our field of view.
posted by Nelson at 6:22 PM on November 1

I'm more interested in the physical frame in terms of what lens would most closely replicate natural vision.

No still lens will. The only thing that could approximate it is a movie camera. The eyes have an incredibly narrow area of focus -- that's why they move so much when you read -- and the image of sight is actually a tiny little bit of focus and a shitload of blur. The brain composites it all into one image, and keeps your eyes roving about to update the image. This is in contrast to even something like a 300mm lens, which will resolve everything across the plane. A tilt-shift lens comes closer, but it's still not the same.

So to get the real effect, what you need to do is shoot a 50mm lens (which gives you a similar perspective to what we see) and then do that thing where you point the camera in every direction without changing the focus and then overlap the pictures. And make them magic pictures that come into focus when you look at them, and blur when you don't.
posted by fightorflight at 6:46 PM on November 1

I'd discovered that my eyesight exactly matches the magnification of a 75mm lens on a full-frame viewfinder. My angle of vision is much larger, however, comparable to a 180 degree fisheye. Thankfully my brain makes things not look so trippy.
posted by klanawa at 7:54 PM on November 1

There are a lot of people, like me, who think a 35-40mm lense more closely replicates what they see with their eyes and therefor find 50mm to be slightly telephoto.
posted by Mitheral at 10:47 PM on November 1

I'm repeating, but I'm still not sure this is clear:

Lenses distort and stretch. A 50mm lense will provide the least distortion. It won't see as wide as we do. I'm not sure any lense does. If you want what you see is what you get, go with 50mm. If you are using a DSLR with a half frame sensor a 28 mm lense will be close to a 50mm lense.
posted by xammerboy at 11:19 PM on November 1

It's complicated. We do not see like a 35mm camera.
Each eye sees a circle, not a rectangle of space, and the two circles overlap mostly, but not 100%.

Our total angle of vision is very wide, like a 20mm lens.

However, we only see sharply with the very center of our vision which is called "the fovia". The sharp area is narrow, say like a 105mm lens. We scan the sharp part around all the time without knowing we're doing it, and we pretend the whole field of vision is sharp.

Argument can be made for lots of focal lengths to say they are natural.
A really wide angle is natural because we can see a wide angle.
A tight telephoto is natural because it matches the sharp area we are actually concentrating on.
Focal lengths inbetween are various levels of compromise between the two ways we see. Some people find the 35mm the most natural, some the 50mm, some the 85mm. There is nothing inherently natural about any of them though. The 50mm being standard is just a convention.
posted by w0mbat at 1:47 AM on November 2 [1 favorite has favorites]

I have 24mm, 35mm, 50mm and 55mm lenses and I tend to use the 35mm 80% of the time (on a film camera). I find the 50mm a little too narrow. To me, its field of view is closer to a stare or focussed gaze while the 35mm is more relaxed.

Still, I sometimes think that the 35mm is a bit wide and that I'd love to have a 40mm or 45mm lens. In this article the author claims that "Using the diagonal of the [35mm] format as the standard, the true normal would be about 42mm." I don't know how he has come to this conclusion but it feels intuitively correct to me.
posted by quosimosaur at 5:25 AM on November 2

w0mbat has it right- an eyeball probably has about a 50mm focal length, but also a very narrow center of clarity- the rest is blurry, but not distorted like a fish-eye. but the combined effect of both eyeballs and our brains processing the data makes our vision much wider.
posted by gjc at 6:13 AM on November 2

gjc, no each eyeball has a focal length of about 17mm focused at infinity. The effect w0mbat is talking about, the ability to change the focal length of our eyes to go from viewing something from far away to something that is close up, is called accommodation.

To confuse things further is you took 35mm negatives shot with a 50mm lens and made a contact sheet the correct viewing distance would be about two inches, if you tried to view them at say ten inches the perspective in the photo's would be off despite being shot with a 50mm lens.
posted by squeak at 7:37 AM on November 2 [1 favorite has favorites]

As a side point, one demo I used to use when I sold cameras long long ago to demonstrate the "normal" aspect of the 50mm lens on a 35mm SLR was to having the customer hold the camera vertically and put it up to one eye, with both eyes open, so one eye is looking through the camera and one eye isn't. Now look around the room. For the most part, people saw minimal mismatch in the size of what they're looking at. The camera eye just looked like there was a window in the way. Hence, "normal" lens.

Try the same thing with a wide-angle or telephoto and there's a big difference.

One of the most useful things I learned in film school was to shoot with a motion picture camera with both eyes open, so I got the peripheral vision of what was going on just outside frame and could anticipate better how to track the subject when shooting tightly.
posted by chazlarson at 8:51 AM on November 2

Optical Engineer here. I'd agree with much of the above: human FOV is typically 180-190 degrees, but the area of interest in your vision is much, much smaller (fovea ~= 2 degrees according to one source; 6 +/- 3.6 deg std dev by another). For reference, a 50mm lens with 35mm film yields a 140 deg FOV (2*acos(17.5/50)).

Finally, your brain reconstructs images with amazing deception, so that fast eye movements reconstruct a larger scene than the fovea actually covers. Thus, while you only really see a few degrees well, you "scan" the area of interest, and your brain fills in the rest. (Try this experiment: hold up a playing card near your edge of vision, while you look straight ahead. If your eyes don't cheat and dart over, not only will the card's value be hard to determine, but even if it is a red or black suit.)

For this same reason, the distortion caused by super-wide-angle lenses & fisheyes are especially troubling: the same effect in your eyes are "corrected in the wetware", and not apparent to your brain.

krilli had an interesting idea:
Pardon my ignorance, but would using an extra-wide panorama-style film and a 50mm lens be closer?


The film would need to follow a more-or-less spherical path; lenses are designed to have a flat focal field (or nearly so), but only over the film/detector area. Since optimization variables are precious few in number, the field flatness is allowed to vary wildly outside of the area of interest. Curved film is actually realizable. If the scene isn't wildly out-of-focus, the resulting picture could be corrected for distortion in Photoshop.

Extra-wide panorama film is not extra-high, however. Your eyes see a spherically-symmetrical field.

OTOH, if the film was out-of-focus at the edges, it might in fact more closely resemble what you actually see. Perhaps that is part of the appeal of LOMO camera pictures...

Final word: recreating the human FOV is ultimately irrelevant to attempting to recreate the experience of vision.
posted by IAmBroom at 9:05 AM on November 2 [3 favorites has favorites]