Physical processes involved when seeing, and comparisons between with other light detection systems. Includes questions about the eye, optical nerve, brain, corrective lenses, etc.

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1answer
489 views

How can you test what color different people perceive? [closed]

If I would show someone a yellow object and ask them, "is this object yellow?" That person would say "yes". But I could never know if my perception of the color yellow is the same as that other ...
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2answers
227 views

Is Invisibility possible according to physics?

Is Invisibility possible according to physics? Is there any backing theory to prove it true or false?
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10answers
14k views

Is it possible that there is a color our human eye can't see?

Is it possible that there's a color that our eye couldn't see? Like all of us are color blind to it. If there is, is it possible to detect/identify it?
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2answers
393 views

Blue-shifting as opposed to violet-shifting

A recent XKCD comic implies that the sky is blue as opposed to violet due to human physiology, and that animals more sensitive to shorter wavelengths will perceive the Earth's sky as the shortest ...
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1answer
89 views

Human eyes vs aberrations

There are no perfect lenses in nature. Aberrations of some kind will always be there. But why healthy human eyes circumvent this issue? Or, are there any aberrations we don't "see?"
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0answers
477 views

Why does the moon look bigger at the horizon? [duplicate]

Possible Duplicate: Why does the moon sometimes appear giant and a orange red color near the horizon? Why does the moon look bigger at horizon or skyline than at other times e.g. at ...
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2answers
3k views

Why do green lasers appear brighter and stronger than red and blue lasers?

This is mostly for my own personal illumination, and isn't directly related to any school or work projects. I just picked up a trio of laser pointers (red, green, and blue), and I notice that when I ...
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3answers
1k views

Why does light of high frequency appear violet?

When people are asked to match monchromatic violet light with an additive mix of basic colours, they (paradoxically) mix in red. In fact, the CIE 1931 color space chromaticity diagram shows this ...
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3answers
1k views

If we had three eyes, would our visual perspective be fourth dimensional?

If one covers up one eye, then he loses depth perception (two dimensional perspective). When we uncover that eye, we can now see depth (three dimensional perspective). My question is if we had four ...
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5answers
2k views

Why is Light invisible?

Why can't we see light? The thing which makes everything visible is itself invisible. Why is it so?
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4answers
9k views

What is the color of a mirror?

A mirror couldn't be white, as then you wouldn't be able to see your reflection so clearly. It wouldn't be transparent, as that then won't reflect. So what color is it?
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4answers
910 views

What colour is nothing?

To me this is very confusing, but I hope we can discuss it and find a solid answer to the question. If you were somewhere where there was absolutely nothing, what colour would your eyes see?
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2answers
1k views

Do we see color with higher frequency first?

Out of the 7 colours of the rainbow, violet has the highest frequency and the smallest wavelength. Does this mean that our eye sees it first? If yes, then why? Does it travel at the same or higher ...
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3answers
6k views

Why is the sky not purple?

I realise the question of why this sky is blue is considered reasonably often here, one way or another. You can take that knowledge as given. What I'm wondering is, given that the spectrum of ...
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5answers
377 views

What are colors?

If you go to any course about photography, you learn that all colors are made up of the colors red, green and blue (RGB). (If you mix red, green and blue light, you will get white light, or any other ...
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1answer
904 views

Static flow of water in the presence of a loudspeaker

The title, I don't know whether it's correct or not, but I came across a video in youtube, http://www.youtube.com/watch?v=_PkgQQqpH2M. The author of video used the title and hence I used the same. ...
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4answers
5k views

Why is there a difference between additive and subtractive trichromatic color theories?

Helmholtz distinguished between additive and subtractive trichromatic color theories. Additive theories concern optical combinations of colored light sources and are usually modelled on RGB while ...
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2answers
875 views

At what distance could you see andromeda with the naked eye?

We've all seen the telescope photographs of andromeda galaxy: I'm wondering if it were possible to travel close enough to the andromeda galaxy could you achieve a same perspective with the naked ...
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5answers
2k views

Explanation about black color, and hence color

I'm bit confused about 'black' as a color. As per my knowledge, it is not given in visible color spectra like other colors for example red, violet etc. Also I'm confused with definition of color--does ...
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1answer
1k views

How do we see different colours?

Why do different wave lengths cause electrons to behave(?) differently, causing us to see different colors? What is happening at the quantum level which causes the colour black to absorb all of the ...
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1answer
3k views

Purple doesn't occur in rainbow - or does it?

Usually, when asked whether the purple color exists rainbows, an answer similar to this is given: The purple color is perceived by human eyes via the activation of both red-sensitive and ...
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1answer
3k views

How much sky do we see at any one moment?

When we look at any particular point the sky, what percentage of the celestial sphere do we see? This question arises from the notion that on average there passes one meteor per hour overhead. So ...
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6answers
6k views

Limit of human eye flicker perception?

I am designing a LED dimmer using software-controlled Pulse Width Modulation, and want to know the minimum PWM frequency that I must reach to make that LED dimming method indistinguishable from ...
0
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1answer
75 views

How to determine the angle a camera has to be at to image a desired scene, given the camera parameters?

Reviewing old material I learned years ago, having a hard time rewrapping my head around the relationships in capturing images from a camera. Imagine a scenario with the camera placed on the ground ...
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1answer
186 views

How does the focal length of the lens change the distance from the camera to an object?

I am reviewing some old image processing notes and have the following problem: I have a camera with a projection plane of $2cm\ by\ 2cm$ and a $15mm$ lens. If you want an $1.5m$ object to take ...
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1answer
1k views

How to determine the field of view for a pinhole camera with given parameters?

I am reviewing some old material I learned years ago and am having trouble figuring this one out. Can somebody confirm that I have done my math correctly, and tell me how I can recover the field of ...
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2answers
2k views

Infrared remote flashes blue light in camera

I know that if you held an infrared remote in front of a digital camera, it'll flash a blue/purplish light when you press the buttons. Why?
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4answers
454 views

What was the motivation behind suggesting the trichromatic theory of vision?

Background In this thread, I asked whether it is true that the colors red, green and blue, through additive mixture, can make up any color. Turns out they can't. However, when reading about the ...
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4answers
3k views

Is it only red, green and blue that can make up any color through additive mixture?

I'm reading about color vision and have some trouble understanding the motivation for why the trichromatic theory was suggested in the first place. The book I'm reading ("Psychgology: The science of ...
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4answers
5k views

Can someone explain the color Pink to me?

I just finished watching this interesting video: http://youtu.be/S9dqJRyk0YM It does a very quick explanation of how pink light doesn't exist, and that the concept of pink is our brain's attempt at ...
2
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1answer
1k views

Effects of high frequency lighting on human vision?

I have a couple of different LED flashlights. One of them has three different "modes" of brightness, and the way it controls it is via pulse width modulation (PWM). Here is a picture that illustrates ...
2
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1answer
350 views

How to determine the required resolution to view an image at a certain size?

If I have several camera specifics, can I determine the required resolution to view an image at the size I want? For example, let's say I want a picture of a square painting to be at least ...
5
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4answers
1k views

Why are color values stored as Red, Green, Blue?

I learned in elementary school that you could get green by mixing blue with yellow. ...
4
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1answer
56 views

Vision vs. limiting magnitude

Does anyone know how the acuity of your vision translates to a difference in limiting magnitude? e.g., the kind of answer I'm looking for would be "For each factor of 2 improvement in your vision ...
6
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1answer
47 views

Refraction and scattered light for NLCs

For helping with judging NLC candidates (are they NLC or not) I have a set of formulas to calculate the minimum altitude (in km) of the candidate given an observed altitude (in degrees) of the ...
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2answers
2k views

Are dangerous rays emitted during Solar Eclipse?

It is said one should avoid staring at Sun as it can damage the eyes, but it is also said that one should not come out in sun during eclipse as it emits dangerous rays. Is that true? If yes, why?
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2answers
145 views

Is there a good explanation for the observation of Martian canals?

Martian "canals" have been observed by independent observers after their first description. Now, they are attributed to "optical illusion", but I think that this is not a good choice of word, because ...
16
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3answers
65k views

Why does the moon sometimes appear giant and a orange red color near the horizon?

I've read various ideas about why the moon looks larger on the horizon. The most reasonable one in my opinion is that it is due to how our brain calculates (perceives) distance, with objects high ...
6
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2answers
2k views

Are regular light bulbs better for the eyes than CFLs or “tube lights”?

I've heard that regular light bulbs with a filament are better for the eyes. Is the spectrum of one worse than the other? If so, are there any regulations for their use in industrial settings for ...
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1answer
5k views

Why can you see virtual images?

In optics it is widely mentioned real images are projectable onto screens whereas virtual ones can only be seen by a person. Isn't that contradictory? I mean in order to see the virtual image it has ...
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4answers
5k views

Eyes open under water

Yesterday I looked underwater with my eyes open (and no goggles) and I realized I can't see anything clearly. Everything looks very, very blurry. My guess is that the eye needs direct contact with air ...
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2answers
263 views

Sensitivity of eye

In which color human eye is most sensitive?