The Human Eye: A Brief Comparison

Kamlan 28mm F1.4 MF for APS-C

12/13/2004 06:03:41 PM · #1

The Human Eye: A Brief Comparison to Photography
by Lee S.

For a while, I had always been interested in how visual optics were equivocal to that of a camera. I always wondered how our eyes could focus without needing to press buttons or without turning a ring. Ever since I got into photography about a year or a year and a half ago, I have been interested in our eyesâ�� field of view and how we focus only on certain things within our field of view and fail to recognize the rest of what is there. This can later be explained in the difference between an initial state of viewing as opposed to the time at which your eyes converge on a detail. However, my first point will start with the aspect of the eye easiest to explain and compare to that of cameras; the aperture.

The aperture of a lens is the diameter of the opening within itself. When measuring apertures in photography, we use an F-number. The F-number is the diameter of the entire lens divided by the diameter of the aperture or opening within the lens (in a camera lens, its diaphragm). Therefore, on a lens with the diameter of 100mm, F/4 would be when the opening is 25mm in diameter; F/2.0 would be 50mm, and so on.
The average eye is ~24mm in diameter, but with a common range that extends from 22mm-30mm. However, the range exceeds even more when we take into account the fact that many people have either hyperopia (farsightedness) or myopia (nearsightedness) in which the eye itself is a different length than a â��normalâ�� eye. Therefore, extended +10 diopters of hyperopia and -30 diopters of myopia, we have the range of eye size of 17.2mm-~36mm based on the formula below (Philipp Pagel).
..............................1.................-2
focal length = ------ = 1.72x10 m = 17.2 mm
.......................58 dpt

Knowing this, we may now calculate the minimum and maximum apertures of the human eye. Based on outside sources, we know that the maximum diameter of the pupil (or our â��diaphragmâ��) to be ~7mm. So based on our formula to get the F-number for a lens we get this:

17.2mm : 7mm = 2.46

So, given an F-stop, our maximum aperture is equivalent to f/2.5.
Now the minimal diameter of our pupil is 1.5mm-2mm and when equated, our minimum aperture is equivalent to F/18-F/25. Thus, our eyes have the aperture range of F/2.5-F/25, which [obviously] changes automatically as a certain amount of light enters. Our eyes do their best to maintain the same amount of light coming in at all times which is why the change in aperture is necessary. However, our eyes do not have shutter speeds; nor does our brain. Just as a computer monitor refreshed every so often, so does our brain; at about 16 frames per seconds. So as our eyes are always scanning and are always seeing more and less light, our brain refreshed and tells our eyes to change aperture. I think of this as pressing the shutter half way down 16 times per second.
As a side-note --- a catâ��s maximum aperture is F/0.9 ;-)

* * *

As for focal length and field of view, some other items need to be touched upon. The following information is based on what I have gathered through research and what I subjectively believe as being the common intuition and philosophy. But before we go any further, we need to forget our magnifying digital sensors and either imagine we are all back to film or that we all just bought ourselves a nice handy new 1DsMII (personally, I prefer the latter)â�¦

If you ask anyone in photography who knows anything about it, they will tell you that a 50mm lens is about the same field of view as what our eyes see. However I have come across that this is not true. Through research and through some time of sitting around with an old manual SLR and a couple of lenses, I (as well as others), have found that the effective angle of view of our eyes is on a ~38mm lens. The standard table of lensâ�� angle of view basically states that the diagonal across the 35mm would be a â��normalâ�� viewing and this comes out to about 43mm so that approximation is not all that off. This approximation of a 38mm relates to when our eyes have not converged and they're focused at infinity. Even though our peripheral vision may extend to nearly 180 degrees, these numbers are within the part of our field of view that is both acceptably focused and recognized by our brain. Someone referred to this moment when your eyes have not converged on a detail as, â��the region of sudden inspirationâ�� and it refers to when you glance at a scene for the first time and your eyes have not yet picked a detail to focus on. Picture walking blindfolded to a spot overlooking the Half Dome in Yosemite. The moment when someone rips off your blindfold and you take in the whole scene at one time is the â��region of sudden inspirationâ��. As for the 50mm thing; this came from the fact that when you close one eye, the field of view is now the same as a 50mm lens. This makes sense for people to have thought this since when you look into a viewfinder, you are usually only using one eyeâ�¦

As for when your eyes pick out details, there is a different â��focal lengthâ��. There seems to be a minimum angle of convergence at which your eyes may not converge on a detail any more acute than that. This is most likely due to the fact that there is a minimum amount of muscle tension that your eyes can take in order to stabilize an eye position. About 80-85mm is the beginning of the region of convergence. On average, our vision can pick out details from this range up to about 135mm (remember this is all in the 35mm equivalent, the numbers have been skewed as there is obviously less focal length, by definition, in our eyes themselves. So the 80-or-85mm to 135mm range has come to be known as the region of stable convergence.

So, in summation, ~38mm is the point for binocular vision as the region of sudden inspiration, 50mm is the point for monocular vision only, and 85mm minimal point in the region of stable convergence. Ever wonder why 28-135mm and 35-135mm lenses are popular? They are popular because they cover the essential range that is â��realâ�� to our eyes and thus, to the viewer of the photograph itself.

So there you have it. Phew! Feel free to ask any questions or correct any mistakes as I know that this is not 100% perfect. Iâ��ve always been just amazed by the physics of things and the reasons why and how things work. I know that I am very enthusiastic about photography and this gives another spin on the old subject. I hope you enjoyed it. Our eyes are the best lenses that we have access to on this Earth. I do think that optically, a hawk would outdo us any day of the week but its all relative so for now lets just think as Canon as the hawk and Nikon the puny human ;-).

Some quick statsâ�¦
The Human Eye:
Aperture Range: F/2.5-F/25
â��Focalâ�� Lengths;
Region of Sudden Inspiration: 38mm
Region of Monocular Vision: 50mm
Region of Stable Convergence: 80mm-135mm

I hope you all enjoyed this little tidbit of information that I put together over the past few days. Please feel free to post your comments and to talk about it --- Iâ��d hate for all of this work to go to nothing! See ya round doods!...

Lee S.

Edit: Some errors!

Message edited by author 2004-12-13 20:11:39.

Manic

DJI Mini 3 Pro

12/13/2004 06:16:35 PM · #2

Fascinating stuff :o) Have you considered sending it to a photography mag or suchlike as an article for publishing? A couple of eyeball photos and the odd diagram would make it perfect...

soup

Canon EOS-30D

Canon EF-S 55-250mm f/4-5.6 IS

12/13/2004 06:27:38 PM · #3

small typo - nor does our brain.

Originally posted by :

nor does out brain. Just as a computer monitor refreshed every so often, so does our brain; at about 16 frames per seconds. So as our eyes are always scanning

interesting info.

Message edited by author 2004-12-13 18:28:07.

Canon EOS-60D

12/13/2004 06:29:48 PM · #4

Are you sure you're only 14? I am SO glad that NY is doing a good job with their education dollars. I'm extremely impressed. :o)

BikeRacer

Canon EF 28-135mm f/3.5-5.6 IS USM

12/13/2004 06:35:58 PM · #5

Really cool stuff!

Just a side-note - there is a group of island (don't remember where) children that free dive and generally spend a lot of time in water who have learned to see well under water. Researchers found that it was that their pupils can get much smaller than most people, and as such, "stop down" to help focus underwater. The researchers tried this on european kids (Swedes, I think) and found that most children under a certain age can train themselves to "stop down" underwater.

FYI

Canon EF-S 18-55mm f/3.5-5.6 IS

12/13/2004 06:52:48 PM · #6

Originally posted by Manic:

Fascinating stuff :o) Have you considered sending it to a photography mag or suchlike as an article for publishing? A couple of eyeball photos and the odd diagram would make it perfect...

Wow! Never thought of that! Interesting... I'll think about it although Im doubtful any mag would be interested :)

Originally posted by soup:

small typo - nor does our brain.

Thanks and done :)

Originally posted by laurielblack:

Are you sure you're only 14? I am SO glad that NY is doing a good job with their education dollars. I'm extremely impressed. :o)

Thanks for the praise Laur! ;-)

Originally posted by BikeRacer:

Wow! Fascinating ... thanks for sharing... I love this kind of stuff...

Thanks!

Konador

Canon EOS-500D Rebel T1i

12/13/2004 06:57:09 PM · #7

Great read... another small typo that popped out at me:

when our eyes have not converged and their (they're) focused at infinity

edit: typo, lol

Message edited by author 2004-12-13 18:59:34.

Zap228

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

12/13/2004 07:00:27 PM · #8

I'm finally beginning to understand how arperature works. Nice article..thing. For some unknown reason, it's actually making sense to me.

12/13/2004 07:11:52 PM · #9

I'm puzzled about some of your figures:

The average eye is ~24mm in diameter, but with a common range that extends from 22mm-30mm. However, the range exceeds even more when we take into account the fact that many people have either hyperopia (farsightedness) or myopia (nearsightedness) in which the eye itself is a different length than a â��normalâ�� eye. Therefore, extended +10 diopters of hyperopia and -30 diopters of myopia, we have the range of eye size of 17.2mm-~36mm based on the formula below (Philipp Pagel).

what is 24mm in diameter? The eye? the pupil?
A rough measurement of my own eye 24mm seems to be the horizontal measurement between the "corners" of the eye. the pupil seems to be appx 3mm (in bright light, but not very bright)
remember 24mm is just under one inch.

I cannot see how the size of the eye it self influences the aperture of the eye, any more than the size of a lens hood influences the aperture of the lens. It must be the pupil itself= the opening of the lens.

Nice read.

Message edited by author 2004-12-13 19:14:33.

12/13/2004 07:22:05 PM · #10

Originally posted by Gauti:

Yes it is the entire eye itself as in a lens' case it is the entire glass of the lens, not the hood. The entire diameter of the glass of the lens divided by the aperture gives you the diameter of the opening within the lens as the same holds true for the eye and the pupil. I think that this answers your question. If it doesn't will anyone else pop in? Also, feel free to reclarify yourself if need be.

Lee

Canon EF 70-200mm f/2.8L USM

12/13/2004 07:35:46 PM · #11

an article in EncyclopÃ¦dia Britannica sheds some light on this, but confuses me more! :)
Hope the linky works for you

edit: some measurements of the eye from above link:

The dimensions of the eye are reasonably constant, varying among individuals by only a millimetre or two; the sagittal (vertical) diameter is about 24 millimetres (about one inch) and is usually less than the transverse diameter. At birth the sagittal diameter is about 16 to 17 millimetres (about 0.65 inch); it increases rapidly to about 22.5 to 23 millimetres (about 0.89 inch) by the age of three years; between three and 13 the globe attains its full size. The weight is about 7.5 grams (.25 ounce), and its volume 6.5 millilitres (0.4 cubic inch).

and maybe a picture:

Message edited by author 2004-12-13 19:37:26.

hsteg

Fujifilm X-T20

12/13/2004 07:39:07 PM · #12

Great work man. Really impressive.

Fujifilm XF 18-55mm f/2.8-4 OIS

12/13/2004 07:44:22 PM · #13

Originally posted by Gauti:

an article in EncyclopÃ¦dia Britannica sheds some light on this, but confuses me more! :)

I understand what you are saying and it is true that there is an average size and length. However I was talking within the capacity of the human eye at its extremes. The worst cases of myopia and hyperopia were used as examples and it varies from individual to individual. So on average you could say that the maximum aperture of a human's eye is equivalent to about f/4 or so instead of the absolute max od f/2.5. Remember, these are just in the most extreme situations in order to make the best generalizations and are not meant to tell what the specifications are for yours or my own eyes. Thanks for bringing up this point. :)

Lee

docpjv

Fujifilm X-E1

12/13/2004 07:50:04 PM · #14

very interesting

rcrawford

Nikon D300

Nikon AF-S DX Zoom-Nikkor 16-85 f/3.5-5.6G ED VR

12/13/2004 08:09:04 PM · #15

Originally posted by Tranquil:

...When measuring apertures in photography, we use an F-number. The F-number is the diameter of the entire lens divided by the diameter of the opening within the lens...

Actually it's the focal length of the lens divided by the diameter of the aperture:-)

Very interesting stuff. With your ability to research and convey information I'm sure you're headed for great thing!!

maxj

Canon EF 50mm f/1.8 II

12/13/2004 08:20:44 PM · #16

holy shit

that was intense

12/13/2004 08:25:00 PM · #17

Originally posted by maxj:

holy shit

that was intense

on brother... rock on... ;-)

12/13/2004 08:26:25 PM · #18

ok. after giving it some thought I'm begining to understand this.
Interestingly if we use the more "normal" values of focal length of 22mm and max aperture of 7 mm we get 22/7 which amounts to 3.142857 or very close to pi (3.1415etc). BTW 22/7 is an old appx of pi for rough purposes.

edit: somewhere in the above EB cite I think I found max aperture of the eye to be 8mm

edit #2:
to clarify (for myself and others)
Focal length: (roughly) distance from front (or out) end of eye/lens to the image produced on the retina/film/sensor. fixed (I think) for the eye and prime lenses, variable for zooms.
Aperture: diameter of the pupil/opening on lens. Adjustable.

see also photonotes.org Dictionary esp focal lenght and F-stop

Message edited by author 2004-12-13 20:33:45.

maxj

Canon EF 50mm f/1.8 II

12/13/2004 08:27:54 PM · #19

was this something you did in your free time or for school?

12/13/2004 08:31:30 PM · #20

Originally posted by maxj:

was this something you did in your free time or for school?

You need to understand --- I have WAY too much free time ... and instead of sitting on my lazy butt, for once I actually did something productive. This was just something that I had been interested in :)

Message edited by author 2004-12-13 20:33:10.

maxj

Canon EF 50mm f/1.8 II

12/13/2004 08:34:23 PM · #21

hats off to ya...that was quite a piece of work

12/13/2004 08:34:37 PM · #22

Originally posted by Tranquil:

Originally posted by maxj:
was this something you did in your free time or for school?

You need to understand --- I have WAY too much free time ... and instead of sitting on my lazy butt, for once I actually did something productive. This was just something that I had been interested in :)

good job, do more of this :)

ps do you do requests ;)

Sigma 18-50mm f/2.8 EX DC for Canon

12/13/2004 08:36:42 PM · #23

LOL Petur! Thanks for the praise ... im burnt out for now ... a couple dollars under my nose may raise my spirits who knows? ;-)
You can always let me know about other things that fascinate you all --- I'm easily fascinated! ... I just take it a little too far sometimes (blush)

Lee

Message edited by author 2004-12-13 20:37:17.

Discraft

Canon EOS-20D

12/13/2004 09:06:51 PM · #24

Great job on that information. Thanks a lot for sharing that with us. We are always learning and this was my lesson for the day. Thanks again and keep it up.