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.

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107 views

Line of vision - If I cannot see someone, is it possible that they can see me?

Imagine I'm on a rooftop of a building. If I am lying down behind a wall and cannot see someone standing on another building- no matter which direction I look, is it possible that they can see me?
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1answer
21 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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1answer
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Why doesnt small optical point source cover whole retina?

This is really noob question, I was thinking about how eye works and I dont understand this most basic thing. Imagine a human looking at tiny omnidirectional source of light, like a small LED diode. ...
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Why does the additive color model use red, green and blue instead of yellow, green and violet?

Long cone cells in the human eye are most sensitive to 570-nm wavelengths which are more like spectral "yellow" than spectral "red" and short cone cells are more to 440-nm wavelengths which are more ...
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Red and orange lights appear to be blinking [closed]

Why does the red and orange lights appear to be "blinking" and the blue and green lights appear to be still? The lights on this hula hoop are always stagnant, and in every picture this exact same ...
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2answers
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How do photons get into the eyes?

I hope you will understand me correctly because there are some things that I translated. It is known that we see the world around us thanks to photons that are reflected from the surfaces of objects, ...
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2answers
99 views

How does a photon impart it's colour to the retina in the instant that it makes contact? [closed]

Considering the speed of light, any number of photons carrying the same colour frequency and hitting the retina at the back of an eyeball would be at varying phases in their respective cycles, but ...
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1answer
56 views

Would 2 people wearing identical night vision goggles be able to see each other from afar? [closed]

From what I understand, this is how night vision goggles (NVGs) function: The environment is illuminated by forward facing IR LEDs. A portion of the light bouncing off of the scene passes through an ...
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1answer
338 views

How do car rear-view mirrors work? [closed]

I wonder, how does a car rear-view mirror work? When there is a car behind me with high-beam, all I do is flip a tong at the bottom of the mirror to relax the lights! Are there two mirrors in it, ...
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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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3answers
182 views

Why is grass green? [closed]

How come grass isn't blue or pink, but apparently, it is according to this scientist it is every color but green. I also got told by my teacher that grass is only green and no other color. So I am ...
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3answers
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How many yellow objects are there? [closed]

I thought and read about color mixing today. I made some counterintuitive discoveries, and i now have some thought experiments which i cannot test. I could print a yellow image but i use a different ...
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1answer
47 views

Simulating the physics of an imperfect eye

I am working on a project where the purpose is to show the most common ocular ametropia (myopia, astigmatism and farsightedness) to lay people. One of the demonstrations I would like to do is: the ...
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1answer
51 views

Can an object at the focal length of the eye be seen?

It is known an object put at the focal length of a convex lens isn't visible since there aren't any light rays that intercept either real or extended. And it is known the eye is a convex lens. So what ...
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0answers
38 views

Do virtual images exist in the real world? [duplicate]

I have been reading an article here in physics stack exchange that talks about if it is possible to see virtual images, and i read an answer saying it is actually your brain that understands the ...
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1answer
54 views

How do we see if light scatters in all directions?

This may be a silly question, but I'm not sure how we see an object in front of us. If light hits the points of the object and scatters in all directions, how come we are able to form an image of the ...
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3answers
85 views

When does the retina fail to recognize images of two closely separated points as distinct?

Our eye is a lens and lenses have a resolving power. The resolving power of a lens, physically speaking, is related to how good two closely separated points A and B can be distinguished as separate. ...
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3answers
104 views

Can Humans actually see 3D Objects? [closed]

More generic, Can an n-dimensional being ever see an n-dimensional object?. It is my understanding that both of our eyes are capturing projections, and without both of them, we will lose our sense of ...
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Why light coming from distant stars is not discrete? [duplicate]

Imaging the light racing out from distant sun, as beam of light shoots aways is a circular pattern (spherical actually), remembering that, light comes in photons or packets of energy. so how come is ...
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2answers
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Why do we see things upside-down when we’re upside-down but not a camera?

If I do a handstand, everything looks upside down (which is originally what we see if we’re upright but the brain switches this). I assume this is because the change in how light rays enter our eye. ...
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Polarised glasses for high astigmatism and myopia [closed]

So I have -4 for both of them, which results in -8 in total (same for left and right eye). At my optician, I have to choose the best package they have to make sure my sunglasses can be as light as ...
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2answers
217 views

Is an obsidian plate safe to use as a Sun viewer? [closed]

Is a 0.5 cm thick obsidian plate good to see the Sun directly?
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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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3answers
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Virtual images - Work of a brain or work of a lens?

I am just a high school student trying to self study, so please excuse me if this question sounds silly to you. Many people tell me that virtual images are formed when two rays that are diverging ...
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2answers
179 views

Can we see a point with only one ray or do we need two rays?

I am just a high school student trying to self study, so please excuse me if you find the question silly. My teacher says that we can see a point when a ray of light from the point is reflected into ...
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1answer
79 views

Is discharge tube dangerous?

Are those gas discharge tubes dangerous? I found atom spectra interesting, so I booked a 1.5 hour lab session at a local high school. The physics teacher gave me a few hydrogen tubes, helium tubes, ...
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1answer
40 views

Yellow color, but not really - does it reflect pure yellow light

This question doesnt relate only to yellow, but basicly to all colors. Lets say: I have pure Yellow painting color and also Yellow painting color mixed from Red and Green. If I would turn on pure ...
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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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5answers
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Why is visible light observed as confined to its source?

When I observe a visible light source, like the sun or a light bulb, why do I observe the light source as a confined object? Like why is the sun or a bulb or whatever seen as a confined ball of ...
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3answers
195 views

Why is the far point of human eye infinite?

In my exams, the presence of this question, which unfortunately I couldn't answer, made me wonder why is the far point of an eye infinite? First thing that came into my mind was that how come we can ...
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Why do cones require more light than rods?

The title says it. In our eyes, why do cones require more light than rods? Like is it because of the energy needed to change the state of the existing atoms, the molecules or what leads to the need of ...
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2answers
65 views

What is the max amount of photons per second of the rods and cones in our eyes?

The title says it all. I just cannot find any information about this - I have tried for so long now. Therefore, I figured that I could reach out to some clever guys in this forum for help instead:) ...
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1answer
50 views

Is there a way to separate 2D from 3D? [closed]

When we see object around us in space, we can always interpret those in 2D, by considering them to pass through a plane, its only when we interact with those objects do we realise that it is 3D, is ...
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1answer
143 views

What are the “real” primary colors and complementary color pairs?

If CMY are the true primary colors of subtractive color theory, are the complementary pairs yellow and blue, cyan and red, and magenta and green the "true" opposite color pairs? For example, a makeup ...
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1answer
84 views

Prescription glasses curved design

Typically, prescription glasses are built with a pair of lenses oriented in a straight line with very little deviation from 180° angle (Figure 1(a)). However, protective or sport goggles (no dioptres) ...
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2answers
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Why are green screens green? [closed]

How/why do green screens work? What's so special about the color green that lets us seamlessly replace the background with another image and keep the human intact? Are there other colors that work ...
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3answers
72 views

Am I right about IR vision?

I watched Kyle's Because Science video on The Predator and 1 thing he talked about was IR vision. Here was his argument: If you can see nothing but infrared light, you can only see the ambient ...
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1answer
132 views

What are the main causes for eyeball becoming too long or short in myopia and hyperopia? [closed]

myopia and hypeopia occur due to change in eye ball size or lack in cilliary muscle ability to accomodate. \n\n But why in lasik laser operation , the one's cornea shape is changed rather than acting ...
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2answers
196 views

How many eyes are needed to see a four-dimensional world? [closed]

If a four-dimensional world were to exist, how many eyes would a creature minimally need to see it (in three dimensions)? Three? Four? (Bonus question: how should these eyes be spatially configured?)...
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1answer
92 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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1answer
60 views

What if our eyes can detect all EM waves [closed]

What if our eyes can detect all EM waves (UV, radio, IR, gamma) along with the visible light. How will our vision looks like then?
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4answers
64 views

Objects and light reflection

We know that we can see objects because of the light reflected by them. But if an object reflects light of wavelengths undetectable by our eyes, will it be invisible?
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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 ...
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1answer
72 views

Can a spinning fan look stationary when illuminated by a flashing light? [closed]

When light flashing rate is the same as a fan’s spinning rate, can you see the fan standing still? I remember reading something like that and can’t seem to find it. Is this incorrect? If so, is there ...
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40 views

EM spectrum and sense of sight

If we cant see all the spectrum does this mean that maybe exist objects we cant perceive? or it just the colors we cant perceive?
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2answers
79 views

Why does purple appear in a rainbow?

It is said that people and digital cameras have color sense only for red, green and blue. So when we see violet/purple in a rainbow, whether with our eyes or in a photo, we should be seeing a color ...
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2answers
53 views

Perception of curvature of human eye [closed]

How are human eyes able to detect the different curvatures of surface ? Basically how are the human eyes able to differentiate between a plane surface and a convex or a concave surface?
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101 views

Why does the Sun appear more round while distant stars can appear more pointed?

In a minute physics video about the shapes of stars, it mentions that stars in the night sky appear star-shaped due to imperfections in our eyes known as suture lines which cause diffraction. Then ...
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2answers
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How can we see stars if their apparent width is less than a pixel?

Stars are so far away that their apparent width is essentially zero when compared to any pixel of a camera or TV screen. And yet we can still see them. According to our eyes stars have a finite ...
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1answer
57 views

Refractive screen for myopia [closed]

Is it possible to create a screen for a computer monitor to allow a Myopic person to see the screen without glasses?