| Author | Thread |
|
|
12/14/2004 06:08:41 PM · #26 |
bump for yall that have eyes.
|
|
|
|
12/14/2004 06:51:55 PM · #27 |
While I agree that comparing the eye to a camera lens is tempting, we have to remember that this is an absolute apples-to-oranges comparison. The purpose of a camera lens is to produce the most accurate image of the world. The purpose of the human eye is to be the front end of the human visual system. The image that gets projected on the retina (at the back of the eye) is nothing like a camera image. For one thing, if the purpose was to produce the most accurate image, we'd need penta-prisms for eyes! Because we have just 'normal' lenses for eyes the image on the retina is upside down, yet we see the world right side up. Why? Because the image at the back of the eye is not what we perceive. What we perceive is partially based on this upside down distorted image, and partially based on innate and learned expectations (like, if something is light blue and huge and featureless and towards the bottom of this upside down image, then it's probably the sky).
There are many other more subtle differences than the image being upside down. I recommend this highly accessible book by Richard Gregory for those who are curious about the peculiarities of human vision, but don't want a textbook. |
|
|
|
12/14/2004 06:57:08 PM · #28 |
Magnus> I was simply making this comparison for a bit of fun andjust to seek out my interests. In no way did i want to prove the best optical system or say that our eyes are cameras. I understand about perceiving things right-side up... People who are dyslexic have a mutation in their genes in which the part of the brain that flips the images we "see" does not function with the same ease as a person without the ailment. I was in no way proposing that we can use our eyes as cameras or to produce "the most accurate image". Just poking some fun at an idea that fascinates me.
Thank you for the link, i will look into that book.
Lee |
|
|
|
12/14/2004 08:22:07 PM · #29 |
Originally posted by Tranquil:
For a while, I had always been interested in how visual optics were equivocal to that of a camera. |
I'd re-write this as "how visual optics equate to ..." or "compare to ..." -- equivocate means to vacillate between two choices ...
The "problem" I have with your explanation is that diameter of the eyeball is only one factor determining focus. The lens, as you can see from that handy diagram, has nowhere hear as large a diameter as the eye. I think to get an accurate F-number, you need to perform the calculations using the relative sizes of the lens and the pupil.
Also, the human lens is not fixed-focus -- it is flexible, and a ring of ciliary muscles surrounding it are constantly adjusting their tension to change its shape and focal length.
As we get older, the lens becomes progressively stiffer, which makes it harder to distort it enough to focus on close-up objects, and eventually leads to age-related farsightedness or presbyopia (Greek for "vision of old people") and the need for reading glasses.
Great article overall ... keep on researching and refining it -- maybe you'd be interested in posting it as a site tutorial?
Message edited by author 2004-12-14 20:25:30. |
|
|
|
12/14/2004 08:54:55 PM · #30 |
Originally posted by GeneralE:
Originally posted by Tranquil:
For a while, I had always been interested in how visual optics were equivocal to that of a camera. |
I'd re-write this as "how visual optics equate to ..." or "compare to ..." -- equivocate means to vacillate between two choices ...
The "problem" I have with your explanation is that diameter of the eyeball is only one factor determining focus. The lens, as you can see from that handy diagram, has nowhere hear as large a diameter as the eye. I think to get an accurate F-number, you need to perform the calculations using the relative sizes of the lens and the pupil.
Also, the human lens is not fixed-focus -- it is flexible, and a ring of ciliary muscles surrounding it are constantly adjusting their tension to change its shape and focal length.
As we get older, the lens becomes progressively stiffer, which makes it harder to distort it enough to focus on close-up objects, and eventually leads to age-related farsightedness or presbyopia (Greek for "vision of old people") and the need for reading glasses.
Great article overall ... keep on researching and refining it -- maybe you'd be interested in posting it as a site tutorial? |
Thanks for the helpful info ... I'll look into that and this is most definitely a "first draft". I had thought about submitting this as a Tutorial but wasn't sure if it would "count" as one. Let me know if yo guys are interested and contact me with details.
Thanks,
Lee |
|
|
|
12/14/2004 09:52:45 PM · #31 |
and I thought I was the only one wondering how aperture and DOF worked in my eyes. That was quite interesting, thanks.
|
|
|
|
12/14/2004 10:15:16 PM · #32 |
This is always good food for thought. In exploring this concept multidude ideas begin to form and seek resolution. For example, the comparison of glass optics to the human eye at first appears as a very plausible exercise but shortly after the digestion of a/b comparisons one finds that the glass optics merely mimics the human eye as much as audio recording mimic real live music. Yes, they always advertise, sound so real that you are transported to a music hall, but not really.
Lens and film create a satisfactory recreation of real life but while the advances continue it all remains a pleasant experience but at no point do we allow the transference of reality into this envelope in a literal manner. The movies offer a dynamic experience but again it is a form of mimic.
All of the above, while extremely good, hardly ever approach the realism it seeks to portray.
Therein lies the problem in the comparison. After a while it is like comparing apples and oranges. The visible spectrum is better represented by the eyes of nocturnal animals, the most common that of cats, owls etc.
Yes, glass optics do an amazing job because note how quickly glass and plastic optics have been used to correct vision, however, while the principle is founded on solid ground, it remains a mimic and a/b comparisons fall short.
This is not to discourage any findings because these exploration reveal to the participants a deeper understanding of the subject matter.
Message edited by author 2004-12-14 22:17:09. |
|
|
|
12/15/2004 06:44:08 AM · #33 |
Originally posted by graphicfunk:
Yes, glass optics do an amazing job because note how quickly glass and plastic optics have been used to correct vision, however, while the principle is founded on solid ground, it remains a mimic and a/b comparisons fall short.
This is not to discourage any findings because these exploration reveal to the participants a deeper understanding of the subject matter. |
Thanks for this tidbit. I definitely agree and I understand your point of view. When you mentioned the movies, it remeinded me of the IMAX cinemas. The screen at these theatres has a certain horizontal space and is curved to make it fit within the better part of our field of view. This is why these movies almost seem three dimensional to us, because we have nothing in our minds telling us that what we are seeing is a two-dimensional screen. The fact that it curves so much makes us feel like we are in the movie. Just a little cool thing i picked up.
However, I also agree that it will be a long time until we ever find a system to correctly mimic our eyes perfectly. I feel that we will do this with audio recording much sooner, for the laws of acoustics and sound are a lot easier to control than that of the eye and brain.
All very good stuff. Thanks.
Lee |
|
|
|
12/15/2004 03:56:45 PM · #34 |
Interesting essay. While the eye is often compared to a camera, I've never seen anyone try to analyze the eye's parameters in camera terms.
One minor error: Someone already mentioned that the F-number is based on the focal length, not the entire lens diameter as stated. Yet the maximum eye aperture was correctly calculated as 17.2 / 7 = 2.46 or about f/2.5. But the arithmetic for the minimum aperture is wrong; 17.2 / 1.5 = 11.47 or f/11. So the aperture range of the eye is not as wide as indicated, just f/2.5-f/11.
And something else to research: The essay discussed the focal length as it relates to field of view (and I need to dig out my old 35mm SLR to convince myself that the numbers are correct). But focal length also affects how the elements of a scene appear in relation to each other. If you take a picture of something fairly close using a 38mm lens, then put on a 150mm lens and back up so that the subject is the same size in the frame, the two pictures will appear quite different. I wonder what the 35mm equivalent focal length of the eye is in this regard. (I'm guessing 50mm, but don't have any data to back that up.) |
|
|
|
12/15/2004 05:37:42 PM · #35 |
Originally posted by dr rick:
But focal length also affects how the elements of a scene appear in relation to each other. If you take a picture of something fairly close using a 38mm lens, then put on a 150mm lens and back up so that the subject is the same size in the frame, the two pictures will appear quite different. I wonder what the 35mm equivalent focal length of the eye is in this regard. (I'm guessing 50mm, but don't have any data to back that up.) |
My understanding has always been that that is exactly why a 50mm lens is considered "normal" on a 35mm film camera. I don't think the "normal" designation was ever about FOV, but rather about the perspective differences as explained by Rick.
|
|
|
|
12/15/2004 05:40:36 PM · #36 |
Did someone say eye?
 |
|
|
|
12/15/2004 05:41:40 PM · #37 |
| That eye reminds me of the eye on Pink Floyd's Pulse album. |
|
|
|
12/15/2004 05:43:49 PM · #38 |
Originally posted by dr rick:
So the aperture range of the eye is not as wide as indicated, just f/2.5-f/11. |
Fortunately, aperture is not the only factor in obtaining a "proper exposure" in the eye, since the retina has a dynamic range probably an order of magnitude more sensitive than any sensor or film in common use today. |
|
|
|
12/15/2004 05:45:44 PM · #39 |
Originally posted by dr rick:
One minor error: Someone already mentioned that the F-number is based on the focal length, not the entire lens diameter as stated. Yet the maximum eye aperture was correctly calculated as 17.2 / 7 = 2.46 or about f/2.5. But the arithmetic for the minimum aperture is wrong; 17.2 / 1.5 = 11.47 or f/11. So the aperture range of the eye is not as wide as indicated, just f/2.5-f/11. |
The minimum aperture was calculated on the ratio of the largest possible "lens diameter" which was 36. So the equation was 36 : 1.5 which equals 26. I was not calculating for the average eye as I stated earlier but as the complete range of possiblities for our eyes.
Lee |
|
|
|
12/15/2004 07:19:19 PM · #40 |
| Finally found a page that summarizes well some of this vision vs photography thing. Ron Dexter over-simplifies lots of stuff, but gets the message across about the totally different functionality of the center of the visual field (the fovea) and the periphery. I know, I know, this thread started with Lee's great essay comparing the optics of the eye and the camera lens, but to me that's just the tip of the iceberg. The fascinating (and really bizarre) stuff is in how we manage to see the world so well with such a mediocre pair of optics. |
|
|
|
12/15/2004 07:45:26 PM · #41 |
magnus> thanks for that link --- it's a little different but still some good stuff in there. It's fine that you posted some other information a little bit off-topic, i actually appreciate it! Great stuff :)
Lee |
|
Home -
Challenges -
Community -
League -
Photos -
Cameras -
Lenses -
Learn -
Help -
Terms of Use -
Privacy -
Top ^
DPChallenge, and website content and design, Copyright © 2001-2025 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 08/09/2025 03:15:50 AM EDT.
