Questions tagged [vision]

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

40 questions with no upvoted or accepted answers
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Glasses underwater

So I figured the refraction of the cornea is based on the index of air and the vitrous humor to make a perfect image. Underwater this is messed with because water has the same index as the eye. Hence ...
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216 views

Does Blue Light Really Have a Dark Side?

I was reading the following article on Wikipedia which discusses the dangers of blue light: Blue-light hazard is defined as the potential for a photochemical-induced retinal injury resulting from ...
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339 views

Can our eyes and ears detect phase information in addition to amplitude and frequency information?

Both eyes and ears detect continuous waves that impinge upon them - electromagnetic waves in the case of eyes, and sound air pressure waves in the case of ears. The amplitude of these waves is ...
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0answers
3k views

What is Curvature of eye lens?

I wanted to know what do we mean by "curvature of eye lens", is it the reciprocal of $r$ i.e $c=1/r$ or is it synonymous to radius of curvature of the eye lens. Moreover how does aperture relate to ...
2
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1answer
33 views

Why is there no blue peak in the photopic luminosity function?

A luminosity function "describes the average spectral sensitivity of human visual perception of brightness". My understanding is that basically, for the same power, we perceive green light as ...
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0answers
628 views

Why do my glasses make the ground look tilted?

I just started wearing glasses to correct my myopia today. I have -0.25 spherical and cylindrical power in my right eye and -0.5 spherical and -0.25 cylindrical in the left eye. Everytime I look at ...
2
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0answers
26 views

Inverting Horizon?

everyone knows that looking at the horizon at something going far away, the last thing you see from it is its top, but what if you had a ground going up very very very slightly and something moves ...
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0answers
74 views

Why do we see vertical lines when we close our eyes into slits?

When we close our eyes into small slits and look at a light source we see vertical lines of light coming out. Why does this happen? Is it something to do with our eyelashes or is it because of ...
2
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0answers
72 views

Why are distant lights more flickery in peripheral vision?

I have just realized that if you arrange your angle to a flickering distant light source and make it fall into your far-peripheral vision (+70 degree to the side of your FOV), you perceive it to be ...
2
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0answers
73 views

Terminology - optical (visual) properties of a structure

I am trying to understand few terminological problems that I encounter. Without knowing keywords it is hard to perform search for literature or publications in the area. The area relates to the ...
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0answers
304 views

Insect Eyes Vs Human Eyes?

Humans have frontal eyes. Less field of view. But better resolving power. Insects have lateral eyes. This means they have a large field of view. In some female insects the lateral eyes have much more ...
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2answers
123 views

Why does image noise happen?

Why are digital images shot with a high iso (which means the camera sensor is much more sensitive to light) so much grainer than pictures taken with a lower iso? Here is an example of the type of ...
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1answer
93 views

Blurred vision clearer with use of 2 mirrors

I have been having trouble with my vision. blurry and shadows. I realized that when I use a hand held mirror to see the back of my hair that is being reflected by another mirror behind my back I can ...
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0answers
48 views

Predict Spectral Composition of Light via the Color Temperature

If I know the color temperature of a given source of light is it possible to predict the spectral composition of the light (in other words the specific wavelengths / frequencies that make up the light ...
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45 views

Do prescription glasses augment or mitigate the effect of the sun on the skin around the eyes directly beneath them (assuming no UV blocking coating)?

The question is about minus correction (nearsightedness), but would also be interesting to know how it differs for plus correction (farsightedness), cylinder correction (astigmatism), axis correction.
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1answer
54 views

Make a projected image smaller?

A friend has a Batman nightlight that projects Batman onto her ceiling. She has vision problems because of a head injury. She could see Batman fine when she was in an upstairs bedroom and the ceiling ...
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40 views

Where can I find CIE 1931 RGB matching functions?

I'm unable to find CIE 1931 RGB matching functions online. Where could I find them (ideally in a tabular form with 1 nm radiometric resolution)?
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2answers
118 views

Colors of the Earth from space, an “average” of particular emitters?

When we're say about 100 km above Earth's ground and look down to it and see the Amazonian region as green, is this green color a sort of "average" of greens from trees from that forest or is the "...
1
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1answer
126 views

What equation should I use to determine retinal image size generated by 10 micron DIA input beam?

If I plot the effective focal spot diameter ($S$) achieved by using the popular expression: $S = \frac{4L}{\pi}\frac{F}{D}$, where L is input beam wavelength, $F$ is the focal length of the lens, and ...
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180 views

What is the minimal size of the spec of dust I can see with naked eye?

When sun directly shines thru the window - I can see small specs of dusts in the air. All specs have different sizes. Assuming direct sun luminosity is 100kLux, spec is a perfect sphere, reflection ...
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0answers
394 views

How do I translate from CIE xyY color space to combinations of monochromatic wavelengths

Let's say I have a chromaticity point, on the CIE xyY color space that falls within the real colors. (Like y:0.1, x:0.4 Y:1 -- magenta)[1] I also know that humans can perceive the same color, when ...
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804 views

Is the human eye diffraction limited, or is there another limiting factor?

I know that most problems involving the human eye in my undergrad physics text book tell the student to treat the human eye as a diffraction limited system (ie to assume the only factor limiting human ...
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270 views

If we increase the aperture of a telescope and decrease its magnification, can it be harmful to the eyes?

The full moon is the brightest object in the night sky. I believe that if we increase the aperture of the objective, and decrease the magnification of the telescope, it might concentrate a dangerous ...
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175 views

How to convert a hologram into an image?

Suppose one knows in full detail the phase and intensity of monochromatic light in a plane. This is basically what a hologram records, at least for some section of a plane. By using this as the ...
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45 views

How to explain this thumb experiment?

Close your thumb to your eyes and align your eyes, thumb and moon. Then focus your eyes on your thumb and watch the moon behind your thumb. You will find that the moon becomes small! Remove your thumb ...
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18 views

Photometry - Photopic and Scotopic vision

I would like to measure the eye sensitivity to a blue LED when a person is placed in a dark room. I need to convert the luminous flux (lumen) to optical power (W). Can someone tell me if I should use ...
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1answer
46 views

How do I explain the below phenomenon I am seeing along the edges of my eyeglass lenses?

I am near-sighted. Here is the phenomenon: I stand in front of a light source that is situated on the ceiling so that it reflects off my eyeglass lenses and appears circular. It is a white light ...
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1answer
57 views

A method for a near/far sighted person to see clearly?

In all the diagrams showing a near/far sighted eye, the image is formed either in front or behind the retina. But what if the person tries not to focus at the object he is looking at? What I mean is ...
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27 views

Derivation of the relationship between snellen rows and diopters

Here's an incorrect derivation of the conversion from rows of a Snellen chart to diopters -- this derivation results in the correct sign but too small a value: Interpret ...
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40 views

Size of an object (the space it occupies in your whole field of vision) as you move away from it

I'm not sure if this is the right forum for this question, and it must be already answered somewhere so you can just point me to the answer. If there is a disc of radius $r$ and an observer is moving ...
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1answer
100 views

How Negative Color Value is accepted in Tristimulus Values for Mixing Colors?

I read a chapter about Trichromatic Theory of Color Mixture (Yao Wang, et all. 2001), about how we can produce most colors by mixing 3 primary colors. And the amount of three primary colors required ...
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12 views

Formula for Vision Acuity and Distance?

Is there a formula that includes distance and Snellen's standard vision system? For example, a person with 20/40 vision can read a letter of a certain size at 20 feet while a person with 20/20 vision ...
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110 views

How do hypermetropic people see objects beyond the focus of their convex corrective lenses?

The way I have developed intuition about optics suggests that humans can only see objects if two rays of light that originally emanated from the same point reach the eye in a way such that when ...
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54 views

Why animal eyes see the spectrum from red to violet?

Maybe this would not be proper question on physics stack exchange, but it originated from physics book so I'll post it here anyway. I have much interest in color recognition evolution. I'm studying ...
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25 views

Why is the focal length of a camera inextricably linked to a different perspective?

The human eye can focus on different distances without ever changing the perspective. Why is the change of focal length in a camera, on the other hand, always linked to a change in perspective? Is the ...
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1answer
52 views

Is light become more lighten in dark places after period time?

Unfortunately I do not have good background with physics, so I may have missed many points in my question. But the phenomenon as follow: When I close my room at night I barely see objects in my room (...
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35 views

Testing UVA and UVB protection in sunglasses?

Is there an inexpensive way to test UVA and UVB protection in sunglasses? (Or does all plastic block a majority of UVA and UVB light?) This question was posed by another StackExchange user in the ...
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269 views

How do these 3D paintings work ? (See the images)

I know that our brain perceives two images from two eyes and combine them to see 3 dimensions and the 3D stuff uses this. But how this works and how can there be two images ? Thanks in advance :)
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696 views

Gaze tracking with the pupil-glint response how does the geometry work?

I am struggling to understand the geometry behind the pupil glint response (see above) (With only one light source). I understand that you use the glint to find the corneal centre (Centre of corneal ...
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1answer
333 views

Why is eye accommodation necessary?

Why is eye accommodation necessary when infinite number of light rays come from a specific point of an object and we can use any pair of rays we need and the curvature of the lens need not to be ...