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A goal in most photography is to present a scene which resembles what a person who had been there at that moment would have seen. Even when intentionally working outside of that, human vision is the de facto baseline.

So, it seems useful to know something about how the eye compares to our camera technology. Leaving aside issues of psychology, pattern recognition, and color perception as much as possible (because that's a separate question!), how does the human eye compare to a modern camera and lens?

What's the effective resolution? Field of view? Maximum (and minimum) aperture? ISO equivalence? Dynamic range? Do we have anything that is equivalent to shutter speed?

What structures are directly analogous to parts of a camera and lens (the pupil and iris, say), and what features are uniquely human (or found in cameras but not biology)?

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+1 i'm also interested. some parts of the question have already been answered in some other more specific questions! –  JoséNunoFerreira Jan 31 '11 at 14:10
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I've made the first question, but I deleted my self because some users started to complain about its subjectivity. I'm glad you could ask the same question in a way nobody complains! –  tomm89 Jan 31 '11 at 16:38
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This is an interesting question but it comes down to comparing apples and oranges in the end. The human eye is highly evolved to deal with the everyday situations that humans have faced over thousands of years. Also, the eye on its own is not analogous to a modern camera/lens system - you must include the brain too (which isn't much more analogous), at which point the camera loses on the grounds of adaptability, speed, usefulness, etc. Also, let's not forget that what a camera produces is pretty useless without an eye/brain to interpret it into something meaningful. –  Nick Feb 1 '11 at 12:25
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@Nick — Absolutely! That's very much the point of the question. Don't forget, apples and oranges can be compared in many different meaningful ways. They're different colors, they taste different, they have different texture, they require different growing conditions, they have different nutritional value, they are used to make different types of products.... –  mattdm Feb 1 '11 at 13:31
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These questions have all been flagged as off topic, however I am not sure that is true. Vision is a key factor in every photographers work, and while not everyone may be interested in these topics, many of us are. I think it is relevant discussion, especially given that we have a lot of technical and science types on these forums. The questions do specifically relate to photography, people are answering them, and there are no votes to close. –  jrista Feb 1 '11 at 16:07

3 Answers 3

(With much help from the Wikipedia article)

Our eyes are a 2 lens system, the first being our outer eye, and the second being a lens just inside of our eye. Our eyes has a fixed focal length, of about 22-24 mm. We have significantly higher resolution near the center than at the edges. The resolution varies significantly based on where in the image you are looking at, but it is around 1.2 arcminutes/line pair in the central region. We have about 6-7 million sensors, thus we have 6-7 megapixels, but they are somewhat different. The pattern of color detectors isn't very uniform, there is different color detection capabilities in the center as compared to the peripheral vision. The field of view is about 90 degrees from the center.

One interesting point is the human eye doesn't ever form a complete "Snapshot", but is more of a continuous system. It can be very hard to tell this, because our brains are very good at correcting for it, but our system is more of a leaky bucket approach to photography, somewhat but not exactly similar to a digital camcorder.

The "Normal" lens is usually chosen to represent the primary area of human focus, thus explaining their differences.

Cameras have different kinds of sensors, but they are usually spread quite uniformly around the sensor. The sensor is always flat (Human's sensor is curved), potentially leading to edge distortions. The resolution is difficult to obtain in the same format as human vision is given, and depends somewhat on the lens, but it can be safely said that the human eye has more resolution in the center of it's focus, but less in the peripheral areas.

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Regarding resolution, which has been discussed a bit on one of my other answers, the 1/60th of a degree (1 arcminute) is for 20/20 vision. While this is "normal" for most people, there are millions of people who see 20/10 as adults. Children also have better acuity, in the 20/10 or even 20/8 range, which is around 0.4 - 0.75 arcminute. –  jrista Jan 31 '11 at 17:34
    
Its not so much that the outer eye is underperforming, its that its doing a different job. The center of the field of view is where we have fine vision, while the outer eye is better for things like low light situations. –  Zachary K Jan 31 '11 at 20:38

Pixiq has a very interesting article on the subject, just released a few days ago: http://web.archive.org/web/20130102112517/http://www.pixiq.com/article/eyes-vs-cameras

They talk about the ISO equivalence, focusing, aperture, shutter speed, etc... It's subject to discussion, but it's still interesting to read.

The eye itself is a good piece of tech, but the brain do much of the work in assembling the pieces together. For example, we can perceive a very large dynamic range, but this is mainly due to the brain assembling the different regions together without us to realize. Same for the resolution, the eye has good resolution in the center, but really under-performs everywhere else. The brain assemble the details for us. Same for the colors, we only perceive colors in the center, but the brain fools us by caching color information when they go out of center scope.

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The human eye really sucks compared to modern camera lenses.

The human visual system, on the other hand, far surpasses any modern camera system (lens, sensor, firmware).

  • The human eye is only sharp in the centre. In fact, it's only sharp in one very, very tiny spot known as the fovea, which is a spot whose diameter is less than one percent of our total angle of view. So we have some serious corner softness going on.

    The human brain is able to correct for this, however. It instructs the eye to make very rapid movements all around a scene so that the sharp part in the middle darts around. The brain then has a pretty awesome in-body image stabilisation, because it takes all these rapid movements and stitches them together to make one, sharp scene - well, at least all the bits the eye landed on while darting around will be sharp.

  • The human eye is quite sensitive to light, but at low light levels no colour information is available. In addition to this, the sharp part in the centre (the fovea) is less sensitive to light.

    Technically it's because the eye has separate photosites called cones for the three colours (red, green, blue), and another different type of photosite called rods that only captures black and white, but is much more efficient.

    The brain stitches all these together to create an excellent full colour image during the day, but even when it's really, really dark it comes up with a soft, colourless image made by all the rods.

  • The eye only has one lens element and it produces terrible chromatic aberration in the form of purple fringing.

    Actually, this fringe is all in the very short wavelengths of light. The human visual system is least sensitive to these blues and violets. In addition to this, it's able to correct for that fringing that does exist in a few ways. First, because the human vision system is only sharp in the middle, and that's where there is the least chromatic aberration. And secondly, because our colour resolution is (outside the fovea) much lower than our brightness resolution, and the brain doesn't tend to use blue when figuring out brightness.

  • We can see in three dimensions. This is partly because we have two eyes, and the brain can do amazing calculations relating to convergence between them. But it's also more advanced than that; as well as the "3D effect" you get from stereo vision, the brain can also reconstruct scenes in three dimensions even when looking at a two-dimensional photo of the scene. It's because it understands cues such as occlusion, shadows, perspective and size clues and uses all these to put together the scene as a 3D space. When we look at a photo of a long hallway we can see that the hallway extends away from us even though we don't have stereo vision, because the brain understands perspective.

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The blind spot is also interesting to mention –  clabacchio Sep 8 at 12:44

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