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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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31 views

Will myopic vision be improved while diving?

Why does my myopic vision improve under water while wearing a diving mask, compared to my normal vision on land?
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How large will my buddy's eyes appear underwater while wearing goggles?

My buddy and I are underwater scuba diving. We are both wearing diving masks. I know an object in the water will appear 1.33 times larger. But how large will my buddy's eyes appear inside of his ...
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Could this work as a way to make 2D appear 3D?

So there is an effect where if you close one eye while watching a 2D movie, it appears slightly more 3D. This being because your depth perception no longer has the cue from two eyes. (As an ...
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34 views

On seeing and especially in the dark

Our retina detects the change in the electromagnetic field due to the jiggling of the atoms surrounding us as I understand the seeing process. In the total absence of a light "source", however, why ...
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36 views

Is their a way to protect screens from being recorded? [closed]

This idea might sound stupid but... Is there a way a screen would be impossible to record using a prism? I’m not talking recorded by a software but recorded from a camera… If you put a prism layer in ...
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33 views

Vision bluriness

I don’t know much about vision so I hope one of you guys could clarify me… When people who have vision problems look at an object without their glasses, they’ll see this object with a certain level ...
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Reverse engineering visible color spectrum with night vision glasses

Here's the context from a discussion I was having with a friend. Let's say I have a picture on my phone. Would it be possible to watch this picture on my phone with night vision glasses who usually ...
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1answer
38 views

How does the eye see a real image?

If we look at a convex mirror diagram, it produces a real inverted image at the bottom. Let's say a person's eye is above the object. How do the reflected rays reach the eye? since it's a concave ...
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3answers
92 views

How do we see virtual images?

Here in the diagram rays coming from B' point falls on two different places on retina of eye.So we should see B' at two different places. But it doesn't happen like that in reality. Is my logic wrong? ...
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Estimating focal length using light

I am considering how to estimate the focal length of a dynamic lens (such as biological lenses) non-invasionally, i.e., without harming the animal. The mammal lens changes its shape depending on ...
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1answer
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Astronauts in spacecraft, they have to circle the earth many times a day, do they also have the illusion of the moon?

Astronauts in spacecraft, they have to circle the earth many times a day, do they also have the illusion of the moon? I don't think they have, because according to the theory, the illusion of the moon ...
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Why can distant objects be focussed more clearly when they are illuminated more brightly?

On a bright summer day, I can look down a straight highway and easily make out signs and some details of typical roadway objects that are at least hundreds of meters away, perhaps a kilometer or more. ...
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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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Is it possible to, using electromagnetic radiation, see the skeleton through a hand with your eyes? [closed]

Using electromagnetic light in the spectrum that can be seen by photoreceptors in the human eye, is it possible to produce an image of the bones onto the human retina?
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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
49 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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4answers
148 views

Is there 100% pure white? [duplicate]

Is it possible to have an object 100% pure white without sky blue or sun color tinting the pure whiteness of the photons reflecting/deflecting off an object? Are there any lights that can produce pure ...
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120 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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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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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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167 views

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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100 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
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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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394 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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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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379 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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196 views

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
55 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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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
56 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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87 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
112 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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1k views

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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65 views

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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388 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
76 views

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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183 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
93 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
65 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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44 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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5answers
76 views

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
350 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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520 views

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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70 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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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 ...