Do eyes compare to Lens

[crayfish13]

So I was bored at school yesterday and I got to thinking whats the aperture of your eyes and the minimum focal length, focal length I understand to be around 50mm. For me my minimum focal length was around 2-3 inches and I figured the aperture to be around f2.8-4. I was wondering if anyone has done any more accurate test to actually determine these values. I understand it wont be the same for everyone but i still think it could be done. I did a quick google search and didnt find anything.

[perryge]

Odd way of thinking about it but here goes.

The eye is roughly 25mm in diameter, so the focal length is definitely smaller than that, probably about 15mm give or take. The pupil varies from about 1.5mm-8mm, making it something like an f/2 aperture that you can stop down to about f/10. Not sure how big the sensitive portion of the retina is (the whole thing is about 35mm, but it's curved), but it'd have a pretty decent 'crop factor' for sure. I did a google search and the fovea has a diameter of 1.5mm.

Ok I looked it up. Focal length is 17mm, retina size is 35mm, fovea 1.5mm. So there's no crop factor in terms of our field of view - a raw 17mm. But since the fovea is only 1.5mm, the area that we can actually focus on is really small, that's a 23x crop factor, so about 400mm. That seems about right really, the field of view we have is very much like a 17mm lens but we can only focus our attention on a little portion of the field, like a 400mm FOV.

Pretty cool that our eyes are pretty much 'full frame'. Don't get the 50mm part confused, a 50mm focal length is said to have a 'perspective' similar to the human eye, not a field of view similar to it.

The cool thing is that our rods and cones are kinda like pixels, and our AF system works in the same way, by detecting contrast.

But our dynamic range is insane and we can crank our ISOs to like, a million, hahaha.

[crayfish13]

Perfect answer to the question, Thanks you.

[yogestee]

Odd way of thinking about it but here goes.

The eye is roughly 25mm in diameter, so the focal length is definitely smaller than that, probably about 15mm give or take. The pupil varies from about 1.5mm-8mm, making it something like an f/2 aperture that you can stop down to about f/10. Not sure how big the sensitive portion of the retina is (the whole thing is about 35mm, but it's curved), but it'd have a pretty decent 'crop factor' for sure. I did a google search and the fovea has a diameter of 1.5mm.

Ok I looked it up. Focal length is 17mm, retina size is 35mm, fovea 1.5mm. So there's no crop factor in terms of our field of view - a raw 17mm. But since the fovea is only 1.5mm, the area that we can actually focus on is really small, that's a 23x crop factor, so about 400mm. That seems about right really, the field of view we have is very much like a 17mm lens but we can only focus our attention on a little portion of the field, like a 400mm FOV.

Pretty cool that our eyes are pretty much 'full frame'. Don't get the 50mm part confused, a 50mm focal length is said to have a 'perspective' similar to the human eye, not a field of view similar to it.

The cool thing is that our rods and cones are kinda like pixels, and our AF system works in the same way, by detecting contrast.

But our dynamic range is insane and we can crank our ISOs to like, a million, hahaha.

Brilliant answer!!

[SkipD]

Don't get the 50mm part confused, a 50mm focal length is said to have a 'perspective' similar to the human eye, not a field of view similar to it...... and anybody who states that a 50mm lens has a 'perspective' similar to the human eye and assumes that's true on various camera formats ("format" refers to the film frame or digital sensor size) is quite wrong.

The 50mm lens is approximately a "normal" lens on a conventional 35mm film camera (one which uses a 24mm by 36mm film frame) or DSLRs using the same size sensor. Other camera formats , use different focal lengths for a "normal" lens. 31mm is the equivalent "normal" focal length for our APS-C DSLRs, for example.

Additionally: Perspective - defined here as the size relationship between foreground and background elements in an image - has absolutely nothing to do with focal length and everything to do with distances between the viewer (or camera) and the various elements in a scene.

[perryge]

..... and anybody who states that a 50mm lens has a 'perspective' similar to the human eye and assumes that's true on various camera formats ("format" refers to the film frame or digital sensor size) is quite wrong.

The 50mm lens is approximately a "normal" lens on a conventional 35mm film camera (one which uses a 24mm by 36mm film frame) or DSLRs using the same size sensor. Other camera formats , use different focal lengths for a "normal" lens. 31mm is the equivalent "normal" focal length for our APS-C DSLRs, for example.

Additionally: Perspective - defined here as the size relationship between foreground and background elements in an image - has absolutely nothing to do with focal length and everything to do with distances between the viewer (or camera) and the various elements in a scene.

^ This man speaks true words of wisdom. I deliberately qualified that sentence with the phrase 'is said to have', and put 'perspective' in quotation marks - I saw this coming from a mile away :lol:.

[JeffreyG]

And to amplify what skip had to say, one also often hears that a normal lens gives about the same FOV as your eye....this is also false.

If you have a 35mm camera with a 1X viewfinder and a 70mm lens then the viewfinder will show your right eye a scene at about the same magnification as what you see with your left eye.

[chauncey]

It sounds like what you guys are saying; a 70mm lens on a FF body "sees" about what the eye "sees", but our "in focus" area is limited to a 400mm FOV. That about right?

Speaking hypothetically here.
And since we cannot crank down the aperature enough (for various reasons) to get everything in focus, we need to shoot our images at 400mm and "stitch" them together to get that 70mm FOV shot completely in focus.
Only trouble is the screwed up depth perception of the 400mm lens.

Sounds reasonable to me, but then I'm a neophyte here.

[SkipD]

Only trouble is the screwed up depth perception of the 400mm lens.There is no "depth perception" or perspective difference for any focal length, long or short. That is a myth that is hard to get folks to forget.

Try this experiment:

1. Put your camera on a tripod and keep it aimed in the same direction for the entire test.

2. Take a series of photos with every focal length you have in the bag.

3. Crop all the photos to match the image taken with the longest focal length. In other words, all the resulting images should have the same amount of the subject material in them.

4. Print the photos to the same size or display them on your monitor at the same size.

You will find that you have a series of virtually identical photos, disregarding the minor differences such as resolution, etc.

The perpective (relative sizes of foreground and background items in the image) will be identical for the shots taken with a myriad of focal lengths. This is because perspective is controlled purely by the distance between the viewer (or camera) and the subject(s).

[chauncey]

I will humbly bow to your superior wisdom in that, no, "all" areas.

[SkipD]

I will humbly bow to your superior wisdom in that, no, "all" areas.A suggestion - do the experiment and then teach others..... ;)

[chauncey]

Will be happy to...just as soon as you lend me your 400mm lens.

[bieber]

http://www.clarkvision.com/imagedetail/eye-resolution.html

[chauncey]

That is a great link!

[chauncey]

To follow up on what Skip suggested;

Is there a standard formula for image reduction that one could apply to a 10MP, 50mm image that would give the same FOV as lets say...a 100mm image or a 200mm image? I know that I could do it using proportions and the DOF calculator, just wanted an easier way.

[pixelhack]

I've just been reading The HDRI Handbook by Christian Bloch. It gets very technical on HDRI and other imaging. He says that the human eye can handle a dynamic range of about 22 EVs (I think that's the number he used), and a camera can only properly expose about 6 EVs in one exposure. That's the difference between a backlit photo with no flash and what our eye sees. Like perryge said above, "our dynamic range is insane...."

Bloch believes that in the near future, we'll have HDRI cameras, monitors, TVs, etc.... That will, I assume, make HDR software unnecessary. If we had a camera that can capture 22 EVs in one shot, that would be SWEET!

[chauncey]

2 Questions to pixelhack-what are EV's and were you responding to my question?

[pixelhack]

chauncey, EV stands for "exposure value". It's the same as one full f/stop or one double (or half) of a shutter speed. One EV higher doubles the light captured in an exposure - like going from a shutter speed of 1 second to 2 seconds with the same aperture and ISO settings. Bloch goes through all the math involved in how they are calculated, but I couldn't quote that right now even if I wanted to. :)

I wasn't necessarily responding specifically to your question. Just commenting on the book. Your comments and others are all related and covered by Bloch's book. I'm not finished with it yet, and I'm just barely scratching the surface on this stuff. If you're interested in HDR imaging, then I highly recommend the book. His companion website for the book is www.hdrlabs.com.

[DrPablo]

The "normal" lens (i.e. 50mm on 35mm film) gives approximately the angle of view of our fovea, which is the area of highest visual acuity.

But our total field of view, including peripheral vision, is around 130 degrees, i.e. wider than any superwide lens other than a fisheye.

If you want to see this field of view on a photographic camera, then do a web search for Noblex pictures, which have a field of view that wide.

[perryge]

To follow up on what Skip suggested;

Is there a standard formula for image reduction that one could apply to a 10MP, 50mm image that would give the same FOV as lets say...a 100mm image or a 200mm image? I know that I could do it using proportions and the DOF calculator, just wanted an easier way.

Yes. Double the focal length, halve the field of view.

[chauncey]

Where else is there this wealth of knowledge where there is always someone that knows the answer.

thanks Perryge!

[bieber]

Yes. Double the focal length, halve the field of view.

Does this mean that we halve each dimension, or halve the area of the field of view (i.e., divide each dimension by the square root of 2)

[perryge]

Does this mean that we halve each dimension, or halve the area of the field of view (i.e., divide each dimension by the square root of 2)

The latter - halve the area I believe. I could be wrong actually...somebody could come and verify or correct this.

[SkipD]

Does this mean that we halve each dimension, or halve the area of the field of view (i.e., divide each dimension by the square root of 2)Double the focal length and you will roughly double the horizontal and vertical dimensions of a subject element in the image on the same size print/display.