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12-02-2009, 12:11 PM   #16
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QuoteOriginally posted by DavidWasch Quote
Just because I hate to leave a question unanswered, the focal length of the human eye is thought to be be 17mm (Reference for FL). The typical range of f/stops for the eye are f/2.1 (for a 7mm diameter pupil) to f/8.3 (3mm pupil on a bright day)-- note this is a bit different than if you were to work it out as you would for a camera, since the eye is filled with fluid rather than air (Reference for eye f-stop).

This information doesn't give us a whole lot, because with the human eye, we do not have fixed 'print' with which to define depth of field or normal perspective. As is stated by the other posters, 'normal' is achieved by simulating relative sizes of objects as they receed into the background of the print-- roughly a 35mm lens on a 35mm camera or a 28mm lens on an APS-C camera when producing on a 4x6" print.

Something pricked at me about your question, too. We always discus normal perspective when wanting to represent what the eye sees, but what about depth of field? If we knew the eye's depth of field, we could then set the 28mm lens to an f-stop that would more closely match what our eyes see.

I fussed around for a little while to see if I could calculate the depth of field for our eyes, and it was HARD! The trouble is that depth of field is intimately related to 'print size', and with the eye, the 'print' is the entire visual field, which is hard to quantify.

I was able to track down a hyperfocal distance of 4 meters (Reference for Eye's hyperfocal distance). Then I turned to the online DOF calculator and plugged in a 28mm lens on a K20D, and then found the f-stop that came closest to 4 meters. The result was f/11.

So, if you wanted to closely represent what they eye sees on a 4x6 print, take a K20D camera with a 28mm lens and shoot at f/11.
I understand what you are saying about the DOF of the and the FOV of the eye...But, lets forget the "Science" for a minute.... This is how I got a few answers in my reply....I looked forward and took both my hands and moved them backward until I could no longer see them in my peripheral vision, Now, the vision beyond 45 degrees or so is very Out-Of-Focus, until you move your eyes in that direction, then the focus is changed to what you are centered on. And what was in focus is now "OOF" because it is now in the peripheral vision. As far as DOF. I think you can do a simple test. look straight ahead and have a few points of focus at 2', 5', 8', 15'. NOW, while looking straight, focus on the 5' object, you will notice the 2', 8', and 15' objects are OOF!...You can refocus on any object at the other points, and the ones you are not focused on will be OOF. Our eye has a limited DOF to what it is focused on, whether we looking straight ahead or to the side. Our FOV may be wider, but the DOF does not extend the FOV. As far as trying to approximate a 4x6 print with the eye. Interesting reading. The Science may be very techical, but I think in real world seeing through our own eyes..a 28mm may be close, but not all of it is in focus, only what we are centered on is in focus.

12-02-2009, 02:43 PM   #17
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QuoteOriginally posted by arbib Quote
I understand what you are saying about the DOF of the and the FOV of the eye...But, lets forget the "Science" for a minute.... This is how I got a few answers in my reply....I looked forward and took both my hands and moved them backward until I could no longer see them in my peripheral vision, Now, the vision beyond 45 degrees or so is very Out-Of-Focus, until you move your eyes in that direction, then the focus is changed to what you are centered on. And what was in focus is now "OOF" because it is now in the peripheral vision. As far as DOF. I think you can do a simple test. look straight ahead and have a few points of focus at 2', 5', 8', 15'. NOW, while looking straight, focus on the 5' object, you will notice the 2', 8', and 15' objects are OOF!...You can refocus on any object at the other points, and the ones you are not focused on will be OOF. Our eye has a limited DOF to what it is focused on, whether we looking straight ahead or to the side. Our FOV may be wider, but the DOF does not extend the FOV. As far as trying to approximate a 4x6 print with the eye. Interesting reading. The Science may be very techical, but I think in real world seeing through our own eyes..a 28mm may be close, but not all of it is in focus, only what we are centered on is in focus.
It is interesting to play with this in the 'real world' I was just checking my hyperfocal distance and it is certainly much farther than 4 meters in the center of my vision. As you indicate, there is considerably more resolution in the in the center of vision than the periphery-- making it very difficult to translate the DOF of the eye to a print.

It's not surprising that much of the writing I found on the eye's DOF related to 3D rendering. In order to make 3D work, the image must have a 'normal' DOF. Most efforts have limited success, and are prone to cause headaches in viewers-- possibly because of the difference between central and edge of field DOF.
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