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77

As mentioned in a number of other answers, there are three different color receptors in a typical person's eye. They respond to different wavelengths of light, as can be seen in the below diagram from wikimedia. The $x$-axis is wavelength in nanometers, and the three curves represent the three receptors' response at those wavelengths. Any incoming light ...


44

The eye is sensitive to light with a wavelength in the range from about 700nm to 400nm, and for the non-colour blind all wavelengths in this range are detected by one or more of the cone cell types. So there are no hidden colours in this range. Light outside the 700-400nm range can't be seen, so I suppose you could claim these are hidden colours, but then ...


21

The reason "myopic" people see Monroe and others see Einstein is that the high frequency information in the image says Einstein and the low frequency says Monroe. When looking at the image closely, you seen the high frequencies and therefore Einstein. By looking at it out of focus (presumably what is meant by "myopic"), the high frequencies are filtered ...


19

You can't see clearly underwater for a couple of reasons. One is the thickness of your lens, but the main one is the index of refraction of your cornea. For reference, here's the Wikipedia picture of a human eye. According to Wikipedia, two-thirds of the refractive power of your eye is in your cornea, and the cornea's refractive index is about 1.376. ...


16

It really depends on what you mean by colour. If by colour you mean "the human brain's response to a given combination of wavelengths", then by definition there can be no invisible colours; wavelengths combinations that do not stimulate any cones in the eye are just equivalent to black. If by colour you mean "a given combination of wavelengths", then we ...


10

We have color perception because we are trichromats. In our genes there is code for three slightly different light-sensitive molecules. The light-sensitive cells in the retina are called cones, and neighbouring cones each produce one of the different versions of the light-senstive molecule. So each of the three cone-types responds slightly differently to the ...


9

This amazing image looks like physicist Albert Einstein. However, move a few feet away from the screen and suddenly it'll transform into Marilyn Monroe. The work of Aude Oliva and her colleagues at the Massachusetts Institute of Technology, the illusion was created in three steps. First, the researchers obtained a photograph of Marilyn Monroe and ...


8

Quickly, try this: Imagine blindingly bright red light! Now blue! Now yellow! You could see stark differences as you shifted from color to color, couldn't you? Yet if you think about what just went on inside of your head, it didn't involve any color photons going into your eyes, did it? So, what you just did must be separate from the light frequencies ...


8

Am I right ? Yes. If so, what lenses should one wear in order to see clearly while under water ? You don't need extra lens you have one in your eyes, just use goggles that makes a layer of air between the water and your eyes. If you decide to put a convergent lens in front of your eyes it won't work because your eye will still not be able to ...


7

This is what I think the first bit of the calculation does. Suppose you start with a spherical eye with a hole in it (e.g. the pupil in the human eye): The radius of the eye is $ER$ and the radius of the hole is $AR$, and with the length $DA$ these form a right angled triangle. Pythagoras' theorem tells us: $$ DA^2 + AR^2 = ER^2 $$ so: $$ DA = ...


6

Dear Rootosaurus, when you're looking at an image of a chair behind you in a flat mirror, then you're observing the so-called virtual image of the chair. If the mirror's surface is located in the $x=0$ plane and the coordinate of the real chair is at $(x,y,z)$, then the virtual image of the chair is at $(-x,y,z)$. However, the light rays coming from the ...


5

The answer is that your eyes would be focusing not at the concrete distance where the mechanism is placed, but at a virtual image which appears farther away. This is just basic optics. It is (one aspect of) what happens when you use a magnifying glass, for instance. The virtual image of some point viewed through an optical instrument is that location in ...


5

The Wikipedia article Aberrations of the eye discusses this. The article is really about non-normal aberration i.e. the sort of thing that makes us have to wear spectacles, but it also mentions the aberrations in normal eyes. The conclusion is that normal eyes are actually pretty good with just a small amount of spherical aberration. The lens and cornea form ...


5

I believe you should have googled first: google hits Especially the second link very clearly explains the main reason: The primary reason why the color red is used for danger signals is that red light is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a color. Therefore blue ...


5

The use of anything but properly designed sunglasses is very foolish and poses great risks to your long term sight, and maybe for reasons that many people do not wholly appreciate. First of all, let's write down what unpolarised light is. We choose two basis polarisation states: let's go with left and right polarised light in this case since you say that 3D ...


4

Unless you deal with holograms, all displays we are observing follow the laws of ray optics. So the display has some specific location – for example, rectangle between four points with certain coordinates – and all the light rays leaving from the points of the display carry the information about their origin because they are diverging from that point, and if ...


4

Color is basically formed in the brain not the eyes. Also the human eye can handle electromagnetic waves from 4000 to 7000 Angstrom, roughly, so called visible light. Above this range, the infrared region is found. It is not red in color or something, it is a name convention. Our eye can not handle it and so the brain dose not recognize it. It is ...


4

Yes, It's true... We know that our eyes have three types of cone cells - S (short), M (medium) & L (large). The naming is done in order to differentiate the cells from "which cell absorbs which color". S to Blue, M to Green and L to red. The peak wavelength of L is 564 nm, yellowish-green. The peak of M is 534 nm, bluish-green. The peak of S is 420 nm, ...


4

This is more of a psychology question. After you start seeing things, you notice that a certain side of your vision is the part that will see your finger if you touch your forehead, and the other side will see your finger if you touch your lips. We designate the first as "up" and the second as "down". The brain just gets a bunch of signals. "up" and "down" ...


4

due to the curvature of the earth, you can only see flat land for about 5km give or take a few hundred meters. from a sky object you are limited by the photon flux emitted or reflected by that object (50-150 photons in a 1ms burst, and all landing within a 10 arcminute spot on your eye) the wavelength of those photons affect your sensitivity (green photons ...


3

I'll add this to the awesome answer from Chris White: People with synesthesia may experience color when stimulated by other sensations, like sounds or letters for example. And some such people have reported seeing "alien colors" that only exist in their visual field when they look at certain graphemes, like punctuation. It is certainly possible that such ...


3

There are different types of color blindness. In color vision tests (patches of color when you can see digits or not) there are some tests where people with normal vision can't see the figure, but people with a specific color blindness can see it. That means people with normal vision are color blind to some specific color differences. It doesn't mean this ...


3

Sadly I don't have a pair of the Google glasses to play with, but I have seen similar things over the years, and these worked as projectors not screens. You're quite right that it would be impossible to focus on a screen in the lens of your spectacles as it's far too close to the eye. However a projector mounted on the glasses can project the light into ...


3

Answer to the additional question: "what is the quantum efficiency of the eye?" I remember old studies reporting that eight photons reaching the photoreceptors can be detected by a human observer as a flash of light in certain laboratory conditions. The more normal range would certainly be lower than 0.125 say 0.05 - 0.01. Cooling down laboratory animals ...


3

Albert Rose studied this question in the 1940's and developed the Rose Criterion which states that the signal-to-noise ratio ($SNR$): $$SNR=\dfrac{\mu}{\sigma}$$ For $100$% identification of an object by the human eye is $SNR \approx 5$. He based this off of quantum arguments where he looked at the average number of photons per unit area in an photo image ...


3

Here are ray diagrams that show what is going on. In the top case, a weak (thin) lens doesn't have the power to pull the rays together tight enough. An object farther away than the tree would make rays converge on the retina. This is farsightedness. Remember the fundamental formula for thin lenses (using some appropriate sign convention): $$ {1\over ...


3

It is not known. Some would even go as far as to say it is not knowable. "Color" is a quale; it is one of those things that may be different from one observer to the other, but both observers will always agree on the name, classification, etc. of a particular combination of frequencies and intensities of the EM spectrum. There is no way to discriminate ...


2

The human retina and visual perception system of the brain display in combination what is known as "persistence of vision." The eye and brain retain a visual image for somewhere between 1/30th and 1/25th of a second, or even longer for especially bright images. See: the Wikipedia entry on Persistence of Vision and the page on The Nature of Visual Perception ...


2

With vision depth is determined by parallax. This largely works for objects out to 100m or less. Depth beyond that distance is assessed by familiarity with these objects, say large mountains or vistas, and experience with them. Depth with hearing is determined by two means. A tone which is perceived louder in one ear than the other is usually perceived ...



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