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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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58 views

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

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
34 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
59 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
37 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
94 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
49 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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67 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
40 views

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
23 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
97 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
50 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
93 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
40 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
58 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
98 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
62 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
48 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
62 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
42 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.
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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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2answers
84 views

Depth of field of the human eye

When reading about the basics of photography and the physics involved, I learned about  depth of field. Long story short, the message is that with a smaller aperture, the length of the depth of field ...
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2answers
77 views

Difference in focus between lenses and glasses [closed]

I have both glasses and contact lenses. The prescriptions are both recent and up to date. I am 46, so I'm starting to have a harder time to focus on things that are very close to my eyes, compared ...
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0answers
33 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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4answers
237 views

How was the Ancient Greek theory of vision disproved?

Ancient Greeks and ancient Indians believed that the way in which vision works is that a beam goes out of the eye and hits an object. Whereas now we know that light reflects off the objects and then ...
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1answer
53 views

Is the anti-blue reflective coating on my glasses doing more harm than good? [closed]

My prescription glasses come with free anti-blue reflective coating. The idea is to minimize the exposure to blue light, which studies have shown can be damaging to eyes over time (especially if it ...
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1answer
27 views

For nearsightedness how does the concave lens not shift the focus point for near objects?

In case of myopia, the light focuses in front of, instead of on, the retina when observing far away objects. while for near objects the eye is able to focus the light onto the retina. For most people ...
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0answers
31 views

How can light bulbs' flicker rates be found? [duplicate]

The flicker fusion threshold is often said to be about $60\,\mathrm{Hz}$ for humans, meaning that humans tend to perceive cycling events happening faster than 60-times-per-second as a blur rather than ...
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1answer
55 views

Why we see a static picture of the sea when we are traveling by plane?

This question may look stupid but it's something that came to my mind months ago when I was on a plane. When one looks through the window on a plane, there are light and dark parts of the ocean (it's ...
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1answer
46 views

How does the human eye not get a distorted image from an irregular object?

Suppose I have a sheet of cardboard, or for that matter any irregularly shaped object. Now we do know that reflection on cardboard is irregular and not specular as it is a rough surface compared to a ...
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2answers
56 views

Human eye dispersion [duplicate]

As we know dispersion is caused by a convex lens.our human eye also has a convex lens so dispersion must take place in eye also this leading to a formation of blurred image on retina.then why are we ...
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1answer
97 views

Colors sensitivity by human eye and light wavelength [duplicate]

I do not understand why human eye sees different colours from the LED TV/screen. Especially violet. For example, how we get yellow color on TV. There are 3 small diodes Red, Green Blue in LED screen ...
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0answers
34 views

Calculate Optical-Ray Angle (in respect to optical Axis) for every Pixel on Sensor Plane

I'm currently working on designing a catadioptric image system for mobile robot systems and do think I need help with the first steps of the calculation. The design of the mirror will be based on this ...
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0answers
16 views

What is the most important data when measuring the 'sources' from which we perceive light?

If the JND of light for our eyes in it's most sensitive areas is easily 5nm or less, when measuring light sources, which data should be most pertinent? For instance, the attached measurement of an ...
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1answer
52 views

Understanding the color of fluorescent and non-fluorescent objects

I am trying to read up and understand a lot about how normal looking objects like chairs are visible to us as compared to fluorescent substances. This question says that - "It is often said that ...
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0answers
23 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

Why does the human eye-lens have a constant magnification for a fixed object distance?

The human eye-lens flexes to change focal length and thereby bring objects of various distance into focus. The magnification of the lens $M$ is always constant for an object with distance $d_o$ ...
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6answers
372 views

Hypothetically, if there was a substance that could absorb all visible light and reflected none, how would it appear to the human eye?

Would said substance just be perceived as a "hole" in our vision, if it was capable of absorbing 100% of all light? Also on a side note, would the absorption of all light instead of only visible ...
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1answer
377 views

Refraction: Swimming goggles, short-sightedness, and underwater vision

I have thought of this question due to personal experience. I am short-sighted, and over the last three years my short-sightedness has worsened. Taking a lifeguard certificate again now that I did ...
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1answer
70 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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1answer
350 views

Dark room lights

When I lay down in my room at night it's pretty much completely dark but I observe this strange phenomenon going on. When I lay down and look at my ceiling I can see my white fluorescent white bulbs ...
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1answer
67 views

Optics and lens

I am nearsighted. So i am using glasses. In glass i see a convex shaped lens. But to correct my vision i need divergengt lens that is concave. When i am using the glass in correct position the upper ...
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0answers
58 views

Chromadepth glasses [closed]

I am making some 3D graphics in POV-Ray that are meant to be viewed using Chromadepth 3D glasses. These glasses make blue objects in a drawing look distant, and red objects look like they're close to ...
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1answer
56 views

What would happen if the aqueous and vitreous humour of a human's eye are replaced by some harmless transparent liquid of different refractive index?

The title says it all. What would the person be able to see? Note By harmless, I mean that it is non-corrosive, non-toxic, etc. The liquid doesn't cause any biological damage to the eye or any other ...
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1answer
61 views

Why doesn't the brain flip retinal image horizontally as well?

I was reading about the Camera Obscura and the physics of apertures, and I read that "The camera obscura produces a flipped (horizontally) image as well as an inverted (vertically) one." I understand ...
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3answers
88 views

What is Fourth Dimension?

Before people get pissed at me for asking a question that has likely been asked more than a few times, I just want to know a simple answer, if first dimension is that an object exists, (collision) ...
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2answers
62 views

I have a question about color and light

I've been thinking, imagine you have a room, a light bulb at the top and you hold your hand up off the ground. Of course, there will be a shadow under your hand and no light will have access to that ...