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71 votes
Accepted

What causes the Sun to appear to be in front of a building in this picture?

You are seeing the effect of a combination of blurring - caused by an imperfect optical system - and saturation. Blurring: ideally, a lens should map a point source into a point source. In reality, ...
Floris's user avatar
  • 119k
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
35 votes

Why doesn't Earth appear smudgy or blurred in space photographs due to its fast rotation?

There are two reasons. The camera might just move at nearly the same speed as the Earth. In this case there is nearly no relative motion and the Earth looks nearly static. The second reason applies ...
Diracology's user avatar
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32 votes
Accepted

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
  • 5,266
30 votes

Why do images not appear inverted when looking directly through a pinhole camera?

Ignoring diffraction, the pinhole can't change the orientation of what you see because it doesn't change the position or direction of any light rays. It just blocks some of them. When you put a screen ...
benrg's user avatar
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23 votes

Is there any advantage in stacking multiple images vs a single long exposure?

Stacking is something that is done all the time in infrared astronomy. This is done because CCD technology doesn't work for wavelengths in the range of roughly 2 to 10 microns, and beyond, so they use ...
Sean E. Lake's user avatar
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23 votes
Accepted

Why can a regular infrared camera not show temperature (thermography)?

This is a common confusion, because both thermographic cameras and "normal" cameras with some IR capability are called IR cameras often. The typical video camera with IR capability has a solid state ...
BjornW'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
20 votes

Why doesn't Earth appear smudgy or blurred in space photographs due to its fast rotation?

I read the other answers and I just wanted to complement them with my photography background. Motion blur in photography is not caused by the high speed of an object. It is caused by the apparent ...
macgyver_sc's user avatar
20 votes

Why do images not appear inverted when looking directly through a pinhole camera?

The directly-through-the-pinhole image is upside down on the retina of your eye. But all images on the retina are upside down. When the lens in your eye forms a real image on the retina it is inverted....
mike stone's user avatar
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17 votes

Why does a pinhole create an image of the Sun?

The images which I remember are the following which show that there is an optimum size for the pinhole but never is the image as sharp as you might expect from that which is formed using a ...
Farcher's user avatar
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16 votes

Is there any advantage in stacking multiple images vs a single long exposure?

The voice of bitter experience, here, to tell you about a problem that a properly working observatory shouldn't have to worry about. But I did the time I was working on a "serious" astronomy project. ...
dmckee --- ex-moderator kitten's user avatar
15 votes
Accepted

Is there any advantage in stacking multiple images vs a single long exposure?

If your exposures are short enough (a fraction of a second), you can even combat turbulence in the atmosphere. The trick is to do very many short images then pick the ones where a (bright) point ...
ProfRob's user avatar
  • 132k
13 votes

Why do images not appear inverted when looking directly through a pinhole camera?

The answer is one about simple geometry and has nothing to do with what happens on the retina or in the brain: you are not looking through a pinhole camera when you are looking through a small hole in ...
AnoE's user avatar
  • 2,698
12 votes

Green dot on photos when taking photo facing the sun

This is probably a better question for photography, not physics. I believe that green dot is a lens flare. It's the effect of the sunlight reflecting off of the optics that, in an ideal world, would ...
Cort Ammon's user avatar
  • 49.6k
12 votes

Why does a pinhole create an image of the Sun?

To directly address your comment: If we place a single point source of light in front of the pinhole then it creates a circular illumination on the screen, but if we put an extended object in front ...
Tanner Swett's user avatar
  • 1,967
10 votes

How can IR cameras see things colder than the camera?

In astronomy, the background from the camera itself is called "dark current" and is removed by first taking an exposure with the shutter closed for, say, half an hour, and then subtract those counts ...
pela's user avatar
  • 10.7k
10 votes

How can IR cameras see things colder than the camera?

By comparing the signal to the background. Suppose you get 10 IR photons from the camera and lens background but an extra 5 from the source then you can still detect the source. There is a whole ...
Martin Beckett's user avatar
10 votes

Is there any advantage in stacking multiple images vs a single long exposure?

I haven't done this for astronomy, but have used an astronomy CCD down a microscope for electroluminescence and have also used cooled imaging CCDs for spectroscopy. Although I have often set the ...
Chris H's user avatar
  • 774
9 votes

Why do images not appear inverted when looking directly through a pinhole camera?

The totality of light that fills space, even in a geometrical optics approximation, is a complicated light field that is difficult to visualize in full. Each point in space generally receives rays of ...
nanoman's user avatar
  • 3,830
8 votes

Why can a regular infrared camera not show temperature (thermography)?

Partly a definition, thermographic means shows temperature - so any camera that shows temperature is thermographic and any that don't aren't ! To measure temperature a camera needs a couple of ...
Martin Beckett's user avatar
7 votes

Is there any advantage in stacking multiple images vs a single long exposure?

I don't know about astronomy, but one reason it can be useful in normal photography is to combat camera shake by auto-aligning the images before blending them. This can be useful if you want to take a ...
N. Virgo's user avatar
  • 34k
7 votes
Accepted

Green dot on photos when taking photo facing the sun

The lens elements in a camera contains anti-reflection coatings (thin films). Although they are intended to remove all internal reflections, they are not perfect. Their effectiveness generally depends ...
flippiefanus's user avatar
  • 14.8k
7 votes

Does a camera have single slit interference?

Here are a series of photographs which were produce by the same camera and lens arrangement but with a different size of the entrance pupil (aperture of the use-d part of the lens slowly). The ...
Farcher's user avatar
  • 96.8k
7 votes

Why doesn't Earth appear smudgy or blurred in space photographs due to its fast rotation?

Any easy way of thinking about it is to realize that your speed relative to the satellite is the same as the satellites speed with respect to you. So it is equivalent to ask if a satellite would look ...
Brian Moths's user avatar
  • 10.9k
7 votes

Why do images not appear inverted when looking directly through a pinhole camera?

You don't see an inverted image by looking through a pin hole because the pin hole is acting as a beam limiting collimator, not a lens - which is to say pinholes do not bend light direction. light ...
traktor's user avatar
  • 171
6 votes

Why do images not appear inverted when looking directly through a pinhole camera?

Has the OP just reduced the size of his pupil by adding another aperture (the pinhole) in front of his eye? A smaller aperture of the will make the scene seem dimmer and if the OP requires corrective ...
D Duck's user avatar
  • 411
6 votes

What if cameras get better than our eyes?

No need to wonder. Hold your smart phone at arm's length. The screen is a digital image with resolution higher than your visual acuity at 1m. If you want to make out its finest details you need a zoom ...
g s's user avatar
  • 13.8k

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