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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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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
83 views

Can Humans actually see 3D Objects?

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
54 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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2answers
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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
52 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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16 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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3answers
56 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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2answers
174 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
51 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
35 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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1answer
33 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
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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
91 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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1answer
106 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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2answers
58 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
47 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
91 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
79 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
7k views

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
69 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
87 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
169 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
70 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
57 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
59 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
69 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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1answer
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
75 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
46 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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2answers
99 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
47 views

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
54 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?
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2answers
87 views

Question about lenses in the human eye

To see near objects,the ciliary muscles contract and the suspensary ligaments loosen,making the lense thicker. İ don't understand how that helps us to see distant objects . To see distant objects ...
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3answers
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How lens works in eyeglasses for distance and near vision?

Consider someone who wears a Contact Lens that is -10.00 diopters in power (very powerful) for distance correction, but needs +2.00 diopters ADD reading glasses "over-the-top" of the contacts to be ...
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6answers
8k views

How does light combine to make new colours?

In computer science, we reference colours using the RGB system and TVs have pixels which consist of groups of red, green and blue lines which turn on and off to create colours. But how does this work?...
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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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2answers
27 views

What is the optimal light setting for human vision? In other words, is my vision better during the day or at night?

There seems to me to be two main effects that should be considered in answering this question. The first is that the iris dilates in low-light settings, which causes an increase in the numerical ...
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1answer
125 views

Why do I see discrete images when moving an object in front of a screen? [closed]

I observed this while doing my homework. I have a habit of shaking my pen between my fingers vigorously while thinking something. My PC's screen is right in front of me (on my study table itself). ...
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1answer
59 views

Can visible light be composed of invisible electromagnetic frequencies?

I know that when we see red light (via electromagnetic frequencies in the red range) and blue light (via electromagnetic frequencies in the blue range) at the same time, we perceive it as magenta ...
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3answers
283 views

Is the yellow we perceive when our eyes are hit by red and green light at the same time the same yellow that is at the yellow frequency/wavelength?

I am trying to understand how color works, and I am curious whether the yellow we perceive when our eyes are hit by red and green light at the same time is the same yellow that is at the exact yellow ...
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1answer
47 views

Why do I see red light reflecting from my normal glasses when I wear anti blue-ray glasses?

Today when I went for eye checkup, the optician presented to me an anti blue ray glasses. This type of glasses reflect blue light, and hence, while wearing my original glasses and holding this new ...
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2answers
61 views

How do our eyes restructure the picture of objects “right side up”? [closed]

I hope I am posting this in the correct site. I am puzzled with the following sentence: Time and space are compressed into a point of no dimension through which images of the things around us are ...
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2answers
107 views

Why cannot we see too small objects with naked eyes?

Why is there a lower limit to the size of objects we can see with our naked eyes? What are the factors at work; diffraction, light reflected, resolution of eyes?
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1answer
4k views

How can we see a beam of light?

A beam of light is made of photons, which simply travel in a line from point $\text{A}$ to point $\text{B}$. But we can only see things when photons hit our retina, so doesn't this mean that the ...
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1answer
66 views

Is light visible? [closed]

I was confused when i saw the rgb spectrum where the light goes on a prism and then we get the colours .. we see the source of the refracted light ? like seeing a blue sun ?
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3answers
67 views

How light help us see objects?

For example imagine we have an object in an area with wind...how the reflected light come to our eyes and doesnt travels with air (medium) ? also can the light be reflected in all directions so every ...
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2answers
76 views

Tiny blue and red paint close to each other result in black or magenta? [closed]

Now, if I draw two tiny spots with red and blue paint on paper and they are so close (but they do not cover each other) to each other that human eyes cannot identify there are two spots. To the color ...
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1answer
44 views

Does looking at someone produce any physical force?

I was driving home one day and it just popped into my head, does looking at someone or something produce any kind of physical force. If someone could answer this question that would be great.