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84 votes
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Could a computer unblur the image from an out of focus microscope?

The blurring is not randomised, it is predictable. See Can someone please explain what happens on microscopic scale when an image becomes unfocused on a screen from a projector lens? for a basic ...
sammy gerbil's user avatar
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82 votes
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A Rainbow Paradox

Yes. It is precisely the larger angle that makes this happen. Because the red is angled "down" more the red droplets are the ones located higher in your field of view.
Dale's user avatar
  • 102k
60 votes

Why doesn't a light ray bend again when emerging from a lens?

They technically should "bend" because of refraction, and a more accurate drawing would be this: But drawings like the one that you show usually just tell you the net effect of the lens, i....
SuperCiocia's user avatar
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46 votes
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What do individual rainbow-forming droplets look like?

First let's zoom into a simulated primary rainbow from a grid of identical droplets, and then dim it to better see the source of color. What you may have noticed is that there're only several small ...
Ruslan's user avatar
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45 votes
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If diverging rays never meet, why do parallel rays meet at infinity?

If you align your viewing direction parallel to some set of parallel lines, you will visually see them ending at some "point" at infinite distance. The typical example is railroad tracks. ...
HTNW's user avatar
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44 votes
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How is a (rifle scope) reticle in focus?

The image of the distant object is formed in the plane of the graticule. The eyepiece is then focused on the image of the distant object and the graticule which is in the same plane. . The ...
Farcher's user avatar
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42 votes

What is this blue thing in a photograph of a bright light?

It is the bright light from the bub reflecting off the image sensor in the camera, then reflecting off the back of one of the lenses and then hitting a different bit of the sensor where it is ...
Martin Beckett's user avatar
42 votes
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How does Fermat's principle make light choose a straight path over a short path?

As others have said, Fermat's principle says that the path which light follows is stationary rather than a minimum of optical path length (though in fact it typically is a bona fide local minimum). ...
Yly's user avatar
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41 votes
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Why doesn’t a normal window produce an apparent rainbow?

It does create the rainbow, but it is almost impossible to notice. When light direction is changed on the glass-air interface - there is always a dispersion : light with different wavelength will ...
BarsMonster's user avatar
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39 votes
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What is this sort of abstract rainbow?

This is not a "rainbow". Quoting from the linked site, "not all colored patches in the sky are rainbows". It instead is a circumhorizon arc. Rainbows are caused by internal by refraction and ...
David Hammen's user avatar
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39 votes

Why doesn't a light ray bend again when emerging from a lens?

You are right. The drawing shown in your question is quite poor. Here is a much better drawing, which correctly shows the refraction of rays on both convex surfaces. The rays bend towards the normal ...
Thomas Fritsch's user avatar
38 votes
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Why is snow white when water has no color?

That's same for cloud, fog, wave splash and so on. Because of tiny size (but in large number) and irregular appearance, reflection and refraction occur in an irregular manner so the light is ...
Ng Chung Tak's user avatar
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38 votes

Could a computer unblur the image from an out of focus microscope?

Yes, it's called deconvolution. Here are some examples of deconvolved images from microscopes: I found these by Googling for "example of deconvolved image from a microscope". It's possible by ...
Octopus's user avatar
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34 votes
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Can one determine the speed of the rain from the shape of the rainbow?

There is a theory of rainbows due to elliptical droplets. It was started by Willy Möbius [1] but is perhaps more clearly described in the modern papers [2,3]. Unfortunately the math is messy. While ...
Anders Sandberg's user avatar
33 votes

Could a computer unblur the image from an out of focus microscope?

Yes, it can be (partially) undone, because the process is not random and only part of the information is lost. Physics You comment that you are interested in the physics aspect of the question, so ...
stafusa's user avatar
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32 votes
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Why does a pinhole create an image of the Sun?

Let us start from the basics. Consider a point source of light placed on the principal axis of the pin hole camera as shown in the diagram below: The point source produces a circular illumination on ...
Vishnu's user avatar
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31 votes
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Reflection of light rays

That's precisely why a single sharp image is formed. Extend all three reflected rays back below the surface to see where the light seems to come from. If your drawing is precise enough, you'll find ...
orion's user avatar
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30 votes
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Spherical mirrors or parabolic mirrors?

Well, the mirrors you are learning in physics are spherical. There are both spherical and parabolic mirrors. The only difference between them is that parabolic mirrors are more precise; they have only ...
The Space Guy's user avatar
28 votes

Why is an arrow pointing through a glass of water only flipped vertically but not horizontally?

Because it is a cylinder, which is a lens, along one axis, and homogeneous along the other. :) As in @fectin's comment: if it were a sphere, rather than a cylinder, then it would flip through the ...
paul garrett's user avatar
27 votes
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How does the mirror know what’s behind the paper?

Perhaps a diagram would help? Excuse my poor artistry: Clearly, you can see that there is a trajectory a ray can take which starts at the top of the egg, hits the mirror, and then intersects your eye....
Riley Scott Jacob's user avatar
26 votes

If diverging rays never meet, why do parallel rays meet at infinity?

Infinity is not a real distance or an actual number. It's used in mathematics when describing limits as a parameter increases without bound. Parallel lines, by definition, never actually meet in a ...
Barmar's user avatar
  • 1,077
25 votes

How can parallel rays meet at infinity?

It means that they don't meet, because as you correctly pointed out parallel lines never meet. Then what's the point in saying "they meet at infinity" if they never meet? Because you can ...
Mauro Giliberti's user avatar
24 votes
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Is there anything to stop an image being projected onto the side walls in a pinhole camera/camera obscura?

By placing a tube in front of the pinhole you should be able confine the solid angle that gets imaged into the room, such that only the wall is illuminated.
Samuel's user avatar
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22 votes

What is this blue thing in a photograph of a bright light?

It's a lens flare of the spiral bulb in the socket. I assume this is the full uncropped picture. Then the bulb and lens flare position are symmetric with respect to the center of the image (in other ...
Jens's user avatar
  • 3,659
22 votes

Why does a pinhole create an image of the Sun?

The important thing is that it is a small hole in the cardboard. (image from Wikipedia (German) - camera obscura) Therefore every point of the original (the sun) produces a small spot on the screen. ...
Thomas Fritsch's user avatar
22 votes
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Where does the "water" come from in a mirage?

The reflected image of the palm tree is accompanied by the reflected image of the sky above and surrounding it. so in the reflection, you see the palm tree and the sky. There is no pool of water: the ...
niels nielsen's user avatar
21 votes
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Is it possible to witness a rainbow while facing the sun?

TL;DR: A rainbow is only visible due to the focusing effects of raindrops, and rays do not get focused unless they reflect internally at least once. The key point that gets lost in most introductory-...
Michael Seifert's user avatar
20 votes
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Pattern in scaled down image of very close lines

The moiré fringes are caused by undersampling, it is the difference between properly sampling a small field of view and undersampling a larger field, it causes spatial aliasing.
Rob's user avatar
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20 votes
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Can a virtual object exist without an observer?

Don't get stuck at the word "virtual", it has nothing to do with the image not being a well defined thing in the physical world. It is just (arbitrary) nomenclature. A real image is one that can be ...
Sebastian Riese's user avatar
19 votes
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How does an endoscope form the image?

Optical fibres can be accurately aligned in an array such that the order of the fibres at one end is identical to the order in the other end to form what is called a coherent bundle. If an image is ...
Farcher's user avatar
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