[ryan s]

I believe it's in Michael Freeman's "The 35mm Handbook." I can look it up a little later if anyone is interested. (IIRC that's where I read it.)

[dosdan]

This is covered here:

Clarkvision Photography - Resolution of the Human Eye

[m8o]

This is covered here:
Clarkvision Photography - Resolution of the Human Eye

Under Focal Length of the Eye he writes "...50 is totally absurd..."

Here is a simple test I want everyone to try. All you need is a zoom that starts in the 30mm range and ends around the 70mm mark. Wider is fine.

A) find an object with high perspective. A chair viewed from 30 - 45 degrees and 20 to 30 degrees down is perfect. Anything with 'perspective' will do. Just don't look at a white wall perpendicular to it no less.

B) Look through the viewfinder at the object with one eye, and keep the other eye open also looking at it.

C) zoom in and out with the lens.

D) notice how the same object shrinks and expands relative to the naked eye. You may even notice a shift of the perspective of the lines of the object (need wider zoom to really notice that)

E) Stop moving the lens barrel when the two views of the object through the two eyes are identical.

F) Note the focal length on the barrel of the lens.

The lens is at or darn close to 50mm, isn't it... A tiny bit under is likely I'd say.

-steve

[amateur6]

This is covered here:

Clarkvision Photography - Resolution of the Human Eye

Brilliant. I want to disagree with all kinds of things that he says (as m80 does above), but that's a GREAT start. Thank you, and thanks again, Peter!

[ryan s]

From The 35mm Handbook:

The complete coverage of the human eye is approximately 240 degrees, although this varies from person to person. However, with the eye in a fixed position, most of the view is fuzzy and ill-defined, with only a tiny spot covering less than 2 degrees being completely sharp.

When the focal length of the lens equals the diagonal measurement of the film frame, the image will appear normal. A 35mm frame measures 43mm diagonally, so theoretically 43mm is normal. In practice, the most common lens (supplied by manufacturers as normal) is 50mm, and any length between 40mm and 55mm will appear free of perspective distortion.

As far as ISO and resolution and such go, our eyes dominate. We use parts of our eyes for day vision and other parts for night vision...we can focus on things inches away to about 6 miles.

A problem with the eye is how un-receptive it is towards light in the blue spectrum. That's why film and (I'm supposing) sensors boost the blues.

That's why the sensors in Sigma cams are called Foveons...cause they have separate sensors for red, green, and blue...just like film...just like the fovea in our eyes

[Arpe]

But don't you have to allow for the processing engine as well? The brain is really good at making things up so you think you see the whole picture, when in fact you don't. Is it 14 bit, 22 maybe? (whatever the hell that means!)

[borno]

The male and female eye seem to be calibrated to a different level also. As an example, where I see natural habitat she sees a messy yard

[falconeye]

Interesting question and most things have been said, already. Some comments:

(1) 9000 x 9000 pixels. At the center of vision, the resolution is indeed 0.47 mm line pair at 1 m distance. That would be 81 MPixel for 120 degree vision.

- Because the center of vision is so small however, the human eye only has a few million dots which aren't evenly spread. So, any digital camera beats the human eye MPixel wise...

- Because the eye can wander around a printed image, you still need a ~100 MPixel image to create the full illusion for the eye to capture, if allowed to be regarded from near enough.

- The eye actually doesn't report pixels to the brain. It reports "features" like lines, edges, etc. to the brain, like it would vectorize the image first Makes comparision even harder...


(2) The human eye has a dynamic range (DR) of:

- 100 (6.5 f-stops) when measured statically

- Eye movements (saccades) increase the range, the human eye performs badly w/o saccades. By how much is difficult to say. Again, if the eye is allowed to wander around a print, the print needs a much higher DR than 6.5 f-stops to create the full illusion.

- The iris (the human eye's aperture setting) allows for a dynamic range of 1,000,000:1 (20 f-stops). The iris reacts within 4 seconds, additional eye chemistry changes are complete after 30 minutes.


So, altogether, digital sensors aren't that bad but don't fool the eye yet because of its many tricks.

[attack11]

That's why the sensors in Sigma cams are called Foveons...cause they have separate sensors for red, green, and blue...just like film...just like the fovea in our eyes

those sensors are only split into 'light' and 'dark' for exposures. i used to own a cam with one (fuji s20pro). they offer a nice wide dynamic range, but the constant mismarketing of twice the actual mp is kinda lame.

[dosdan]

m80, the problem with a 50mm intra-ocular FL is that the distance between the lens & retina is 22-24mm. See:

http://galileo.phys.virginia.edu/classes/531.cas8m.fall04/l11.pdf.

Standardized Human Eye

So if the FL inside the eye was 50mm, the image would not be in focus by the time it reached the retina.

[khardur]

anything faster than around 60 frames per second is indistinguishable to the human eye (thats why most monitors have a base refresh rate of 60fps, <snip>

Sorry, but I believe this is wrong. Can the human eye distinguish between 60 fps and higher? Maybe not in the short term, say, a few seconds. But talking about monitors - I can tell within seconds sitting at a monitor if it's at 60hz. (I'm talking a traditional CRT monitor - the LCD's are more comfortable to the eyes @ 60hz)

Try sitting in front of an older CRT monitor @ 60hz for a few hours and see if your eyes start to bug you. Crank it up to 75 or 85hz and voila, it feels better. Maybe the eyes themselves might be hard pressed to distinguish it right off, but in the "post processing" it makes a difference.

Sure, it may sound rediculous when gamers brag about getting 100+ fps, but that's a little different of an argument. When the cpu/graphics card really get bogged down they're probably getting closer to what the monitor is refreshing at, so they're happy they don't get flicker even in the most graphically intense areas of their games.


As far as the the original question: f-stop, without reading the linked articles above, my first guess is that this isn't really a valid comparison of the two. The eyes are so much more intricate ofa design, and the post-processing in the brain has a lot to do with what we see. Try this:
Look at your computer screen. Now look at something at the edge along the left side. Using your peripheral vision, take in what's on the right side of the screen. It's fuzzy isn't it? And certain colors don't even seem to show up right. I'm going to say your eyes are more like lensbabies, if you really need to compare them to lenses: that is it's subjective focus, and anything you're not focusing directly on is going to be blurry, no matter if it's the same distance from your eyes or not. So there's a certain angle that's in focus, then the rest is half-processed and discarded by the brain as irrelevant at the time, with the exception that motion in the peripheral area catches your attention (to avoid that bus you were about to step in front of).

There's my explanation.

[khardur]

E) Stop moving the lens barrel when the two views of the object through the two eyes are identical.

F) Note the focal length on the barrel of the lens.

The lens is at or darn close to 50mm, isn't it... A tiny bit under is likely I'd say.

-steve

wouldn't the size of the viewfinder make a difference in this? Say, if I did the same experiment with my K110d which has an 85% magnification viewfinder, and a K10D, which has what, 95% magnification? But I don't know the answer, since I don't have a K10D. I wouldn't mind knowing the answer from someone who has both a K10D and a K100D - do the above test and see with the kit lens and see if you come up with different values based on the different magnification on the viewfinder.

So m8o, back to your idea though - I would say perhaps your lens test would be like saying an aps-c sensor is like a 35mm frame with the outer edges cropped out. That is, the 48mm or whatever you come up with is like the eye's natural magnification, but cropped.

*shrug* I shouldn't pretend to be thinking straight at 1am, sorry!

[m8o]

m80, the problem with a 50mm intra-ocular FL is that the distance between the lens & retina is 22-24mm. See:
http://galileo.phys.virginia.edu/classes/531.cas8m.fall04/l11.pdf.
Standardized Human Eye
So if the FL inside the eye was 50mm, the image would not be in focus by the time it reached the retina.

I certainly have never studied the subject. Is consideration given that a lens is a very different substance then an eye, the latter being mainly water? And the surface dimensions of the eye's lens and retina? You seem to be equating a formula used for camera optics onto a plane to the internals of the eye. It seems the math surrounding any dimensions and lengths that go into the optical calculations of the internals of the eye are going to differ then those of a camera lens and the surface capturing the projected image out of necessity due to composition and structure.

The 50mm equivalence is "plain to see" by the sequence of steps outlined above. I'm not saying a 50mm lens through a 35mm film camera viewfinder, let alone 1.5x cropped D-SLR viewfinder is the same FOV as the eye (something way too many people confuse with perspective)... but it is quite observable that the perspective and magnification (5% error caused by the less then 1x magnification of the viewfinder notwithstanding) is the same at that focal length. Go ahead and explain otherwise as to why we shouldn't believe our own eyes.

What's even more notable is looking at both a close object and distant object with the eyes...
- noting the size of the object off in the distance.
- Look at the two objects through lenses from anything like 10mm to 500mm
- move your position so the object close to you remains constant in size
- note the size of the object off in the distance.

I already know at what focal length the object off in distance through the lens is the same size as with the naked eye; and where I'll be standing in the same spot when keeping the near object constant, looking both through a lens and without.

[m8o]

wouldn't the size of the viewfinder make a difference in this? Say, if I did the same experiment with my K110d which has an 85% magnification viewfinder, and a K10D, which has what, 95% magnification?

It does. With 0.95 mag if we find our lens barrel is at 50mm after the experiment that equates to an error of 2.5mm. We can live with that and factor it in (subtract it) from the position we find the lens in after the steps. It entered my mind but I was "keeping it simple". I didn't at all realize the K110D had a 0.85 mag viewfinder.

Yes, the cropping won't enter into this in the slightest if you try it. Just line up any of the the lines/square/outline of the object you are looking at that are not cropped out by the viewfinder, when the dimensions through the lens are the same as your naked eye. I found I always hit right on 50mm when I do that. With the 0.95 viewfinder mag, we hit that 48mm you mention (47.5 rounded off). Yes, you're thinking very clearly. time for me to hit the sak too being in the same timezone.

[Katsura]

I do not agree.

Maybe it's because I'm more sensitive to flickering, but I can distinctively tell the difference between a monitor set to 60Hz refresh rate and 90, I can also tell the diff between 60 and 70 and 85, above 85 I can no longer tell the difference.