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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727 views

Resolution of the Eye-Light Rays and Diffraction

Please look at the problem. The problem is solved for me. However, I don't understand why the angle alpha is considered to stay constant when the rays go through the lens. The ray along the distance ...
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1answer
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Visual Fields testing: Decibels of sensitivity - meaning

Automated Visual Field test measures the patient light sensitivity in decibels. Questions: If one point has sensitivity of 30 decibels and another point has sensitivity of 27 decibels does it mean ...
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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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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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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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147 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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1answer
101 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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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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112 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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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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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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67 views

Why does violet (purple) color contain red component? [duplicate]

We see rainbow color on short-wavelength side as violet or purple: And this color is obviously contain R component from RGB. How can this happen, if only blue pines can percept this color, while red ...
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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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464 views

What would the rainbow look like if we could see the full EM spectrum? [duplicate]

Would the rainbow look different if we could see the full EM spectrum (or at least a lot more of it)? Would the width of a rainbow be bigger and would all wave lengths of light be in a rainbow?
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47 views

Chromatic aberration in human eye [duplicate]

A lens focuses the different colours of white light at different points. Since our eye has a convex lens there should also be such an aberration but we see objects clearly with normal eye. I want to ...
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1answer
799 views

Why does the sky look blue rather than violet? [duplicate]

Sky looks blue because because our eyes are sensitive to blue colour. But when viewed through a camera why don't we see violet of the sky even though we can see violet colour of other pictures taken ...
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697 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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2answers
403 views

Perspective Redux (why objects seem smaller as the distance increases) [duplicate]

Last time I brought this up, the best answer featured an image that looked something like this: The argument here is that as the distance increases between the eye and the object, the angle gets ...
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1answer
7k views

How fast would you have to run to create a mirror image? [closed]

So I was watching The Flash and in the most recent episode he runs so fast that he is able to create a mirror image of himself so that it looks like there is more of him than there actually is. So I ...
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2answers
104 views

How am I able to tell whether it is dark or not while eyes closed? [closed]

How am I able to tell whether there is a light on in front of me even with my eyes closed? The usual darkness whilst eyes closed transforms into a not so bright glow when my closed eyes are in front ...
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54 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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1answer
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Why can I look at the sun with my sunglasses but not at the solar eclipse?

Is the problem with seeing an eclipse that you have a sudden change between penumbra and regular sun? If that's the case, why can I look to the sun with my sunglasses on but I can't do it in an ...
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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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3answers
247 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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1answer
54 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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1answer
55 views

How can I get the sensitivity of some eye cone at a specific wavelength?

The following graph shows the sensitivity for eye cones and rods, but I want to know e.g. what is the red cone sensitivity for a wavelength of 500 nm? How can I find an answer for questions like this?...
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322 views

Can a high-watt laser's scattering light be damaging to the eyes? [closed]

Heyo, I recently purchased a S3 Arctic Class IV laser pointer. I bought the 3500mW. (In case that page expires, it's 445nm wavelength, 1.5mRad variant, NOHD is 279m, beam distance at 0.25 Lux 72km.) ...
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1answer
224 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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1answer
335 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 ...
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1answer
141 views

How dark is our universe(space) to us?

Yesterday I made a few photos from ISS and then made this aweseome gif out of them. If one would go out at night, where are no disturbances of city lights, one would see a bright, black, starry sky ...
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2answers
43 views

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
62 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
60 views

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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42 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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1answer
89 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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2answers
64 views

Are we always inaccurate or relative about the real size of an object?

So basically the further we are, the smaller an object appears and as we get closer to it, it enlarges progressively, is it so that the size of an object is always relative and that we can never ...
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1answer
85 views

is it possible to extract spectrum (color in general) from an animal [closed]

if i may ask....can this be ASAP? :3 my problem: okay this is going to sound lame, but i was wondering if it is possible to extract color (specifically spectrum) from an animal. this question ...
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2answers
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How do we see the sun?

This question was originally posted almost a year ago and it was misunderstood probably because of its wording. I understand my question better now. Let me put the question this way now: If possible ...
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How is high intensity visible light able to produce an image of the bones onto the human retina? [duplicate]

How can high intensity visible light produce an image of the bones onto the human retina? With scattering, even with high intensity light, would there be enough contrast between the bones and the ...
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1answer
82 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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1answer
112 views

Is visible light really visible? [closed]

As we know, colors only exist in the brain. How can we see light if it has no color? Our eyes detect light, but seeing occurs in the visual cortex. Is visible light really visible?