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03-27-2010, 07:49 AM   #1
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Closest to the human eye?

This might be a dumb question but, is there a specific focal length that is closest to the human eye? as in perspective and angle? I don't think I have learned this yet, or have forgotten. I'm going to take a guess though, on my K-X 50-55 seems closest to me. Might be difference on DSLR and SLRs...

03-27-2010, 11:08 AM   #2
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You'll get different answers, depending on the respondents' perspectives.

Human binocular vision encompasses about 140 degrees; on your Kx, that would be around 6mm (SIX!). Yup, a rather wide angle of view (AOV). In some formats, 'normal' focal length for 'normal' AOV is calculated as the diagonal of the film/sensor frame; on your Kx, that's 30mm for about 50 degrees. Some consider that a "wide normal" and would insist on 35mm for about 45 degrees. If your attention is focused on something, you might ignore peripheral subjects and have an AOV of about 30 degrees; on your Kx, that's a 55mm lens. And if you have "tunnel vision", you'd be comfortable with a 85mm lens for an AOV around 20 degrees.

But human visual perception isn't like a camera's. Your internal image-processing system is both telephoto and ultra-wide-angle, with infinite depth of field (DOF). That's why snapshots of scenery are often disappointing; the camera reports on what it sees, not the composite image your brain has synthesized. Which just means that any photo that doesn't seem too distorted, will seem 'normal'.

Hope this helps.
03-27-2010, 11:10 AM   #3
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Is this before or after a joint?
03-27-2010, 11:32 AM   #4
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There are other posts on the forum with technical answers to the question, but I don't see how 50-55mm on a dslr is even close to a possible answer. I think you can make a case for about 6-15mm on a crop sensor, or the correspondingly larger numbers on 35mm full frame.

Paul

03-27-2010, 11:43 AM   #5
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It's not a dumb question, but it's one that leads to an *incredible* degree of confusion. What you are asking is about the concept of a "normal" lens. browse this is the lens forum for hundreds upon hundreds of posts debating the topic.

The human eye does not have a special perspective, nor does any lens. All lenses (well other than fisheye lenses) have *exactly* the same perspective. Perspective is a function of your position relative to your subject, period. The only reason people ever got it in their head that different focal lengths have different perspectives is that onger lenses typically make you stand further from your subject.

Some people also make the mistake of associating focal length with how big things look in the viewfinder, but that is as much a function of the viewfinder itself. With a larger viewfinder, you'd need a shorter lens to get the same magnification; with a smaller viewfinder, you'd need a longer lens. So there is no one special focal length that matches the eye - it depends on the viewfinder. But with the viewfinder on your K-x, it would be about 60-70mm.

So angle of view is all there is to it - there is nothing else worth looking at in talking about what lens might be close to the human eye. The angle of view human eye is *much* wider than what you get from 50-55 (on APS-C or 35mm film). Stick your 18-55 on your K-x, and you'll see that you can actually take in more than even the 18mm setting. Of course, much of that is peripheral vision, but there is no hard and fast dividng line between peripheral and non-peripheral vision. Most would subjectively that a focal length of somewhere around 35mm on APS-C most closely approximates the amount of a scene they are aware of. but it's impossibe to determine an answer objectively.

What you *can* objectively is define normal in terms of a print. If you print an image, then view the image from a typical distance for that size print (the bigger the print, the greater the viewing distance), a "normal" lens is one that has exactly the same angle of view as that of the print when viewed from that distance. There is room for subjectivity here too - how far is a "typical" viewing distance - but the consensus is that a focal length equal to the diagonal of your sensor is about right. For APS-C, that's about 28mm.

Last edited by Marc Sabatella; 03-27-2010 at 11:56 AM.
03-27-2010, 11:46 AM   #6
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QuoteOriginally posted by Ira Quote
Is this before or after a joint?
Before the joint, before the peyote (which improves colors tremendously, or so I've read), before the glue, but after the first cup of coffee.

Wait, there's a trick to this question. OP didn't ask about human vision, but the human eye. (WARNING: Don't look into laser with remaining eye.) Anyway, if I close one eye, the remaining eye sees about 90 degrees, which is the AOV of a 14mm lens on APS-C. And pentax just happens to make a 14mm lens! Coincidence, or... ????
03-27-2010, 12:39 PM   #7
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A non-technical answer :)

Hold your camera with a lens mounted on it.
Keep both your eyes open.
Look at a scene with one eye in the normal operation mode (!) and the other thorough the viewfinder.
Compare the relative sizes of the objects you see (or compare the perceived distances).
In only a very narrow set of focal lengths you will see that they are the same.
That focal length "for you", is the one!
The kit lens covers all the potential focal lengths in this regard; so, just play with that.
You will be surprised to see that "for you", it will always be the same focal length.
You will notice that at 50mm the image on your camera side will be larger.
You will also notice that at about 35mm the image on your camera side will be smaller.

For me, 40mm is perfect.
For others it may be 43mm.
These values will not change much, even for the visually impaired people; values smaller than 35 and bigger than 50 are highly unlikely, if not impossible.
03-27-2010, 01:35 PM   #8
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QuoteOriginally posted by RioRico Quote
Your internal image-processing system is both telephoto and ultra-wide-angle, with infinite depth of field (DOF). That's why snapshots of scenery are often disappointing; the camera reports on what it sees, not the composite image your brain has synthesized.
Lovely! Very well said

03-27-2010, 02:04 PM   #9
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On our digital cameras, around 35-40 mm is considered "normal". Marc's answer is right on in that our eyes have a much wider angle of view than a "normal" lens. Also consider that our brains can focus our attention on a very narrow part of that field of view. When we look at a photo, our attention is focused on the whole photo. I have difficulty shooting landscapes because I can rarely produce a photo with the same scene my brain remembers. I guess that's why I prefer to shoot sports. I can focus in on the action.
03-27-2010, 02:19 PM   #10
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QuoteOriginally posted by Ecaterin Quote
Lovely! Very well said
Thanks much! My readings in human cognition suggest that large portions of our brains are dedicated to building mental maps -- taking (heavily filtered) inputs, mixing them with memory and expectation, looking for known or hoped-for (or feared) patterns, and building mind-pictures. Unless we consciously bypass some of the filtration and put aside our memories, we see what we expect to see and don't see the unexpected. (I'll cite the famous study of an audience watching a basketball team toss a ball around, not noticing the guy in the gorilla suit cavorting in the background.)

Even color rendition is affected. I'm always surprised when I shoot something by available light in my dark-green cedar forest, whether directly sun-lit or not (and lit from various angles), with various lenses, and the captured image is much more saturated-blue than I 'saw'. Those same lenses in non-forest locales may be just as saturated, but not so blue. My visual system is obviously setting its own white balance. If I can't even 'see' the blueness, it's no surprise that I didn't notice the giant praying mantis peering over my shoulder, eh?
03-27-2010, 02:55 PM   #11
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Wow, yeah I have thought about it like how some of the answers explained. I should have been a tiny bit more specific, and I used the wrong words to describe what I was getting at... I meant when I looked at around 50-55mm the object in the viewfinder was as big as when I looked at it without the viewfinder. I know it can never match our FOV... Yeah... Interesting read guys, thanks for trying to answer. I just confused myself...
03-27-2010, 03:06 PM   #12
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PBS has a free documentary you can download on fractals, and in that film, they spend a great deal of time talking about human vision and its reliance on fractal geometry allowing us to read, and to take in a large scene in great detail. I seem to recall they point out the actual detailed section of our vision is very tiny compared to a "camera", but the fractal scanning pattern generated by our brain yields the wonder images we take for-granted as vision.
03-27-2010, 03:33 PM   #13
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From Handbook of Optical Systems: Vol. 4 Survey of Optical Instruments. Edited by Herbert Gross
Copyright 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
ISBN: 978-3-527-40380-6
Chapter 36 Human Eye

eye fov -- maximum is 108 degrees; fovea is 5 degrees, however the entire macula lutea is ~3x foveal diameter, thus "normal" fov is 18 degrees.

16mm lens on 35mm film camera has about 108 degrees fov.

500mm lens on 35mm film camera has about 5 degrees fov.

150mm lens on 35mm film camera has about 16 degrees fov.
03-27-2010, 03:49 PM   #14
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QuoteOriginally posted by rhodopsin Quote
eye fov -- maximum is 108 degrees; fovea is 5 degrees, however the entire macula lutea is ~3x foveal diameter, thus "normal" fov is 18 degrees.

16mm lens on 35mm film camera has about 108 degrees fov.

500mm lens on 35mm film camera has about 5 degrees fov.

150mm lens on 35mm film camera has about 16 degrees fov.
Translated for APS-C:
~10mm lens for 108 degrees FOV

~85mm lens for 18 degrees FOV

300mm lens for 5 degrees FOV
None of these is anywhere near what we talk about as 'normal' lenses. Sigh. Why can't we have more normalcy around here?
[NOTE: Don't confuse FOV with fovea.]
03-27-2010, 03:53 PM   #15
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QuoteOriginally posted by RioRico Quote
Translated for APS-C:
~10mm lens for 108 degrees FOV

~85mm lens for 18 degrees FOV

300mm lens for 5 degrees FOV
None of these is anywhere near what we talk about as 'normal' lenses. Sigh. Why can't we have more normalcy around here?
[NOTE: Don't confuse FOV with fovea.]
Haha thanks, and... CONFUSION AGAIN... ;( The human eye is magical, that's why.
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