# Tag Info

73

[Caveat for this answer: it (both parts) is almost literally a transcript of a back-of-the-envelope calculation: there may be mistakes.] The calculation for a distant camera not co-rotating with the Earth A 50mm lens on 35mm film has about a 40 degree angle of view. Let's assume we're pointing that lens at the Earth so the Earth fills this angle of view, ...

71

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, it is mapped into something slightly wider than that. If the image is well-focused, the lens is free of imperfections, and diffraction due to the finite size of ...

44

The sun is still surprisingly bright at Pluto. While it is approximately 1500 times less bright than at Earth, this is still approximately 250 times brighter than a full moon. If you consider the effect the difference between a full and new moon has on star viewing I expect that the reflected sun at Pluto is still bright enough to make it difficult to see ...

43

I've worked on a camera that has as one of its core features the ability to increase the FPS until you are counting single photons. Here is one of the pdfs about it. You will see from the figures that there is an intrinsic tradeoff between the noise/image-quality and the FPS, which is simply due to the statistics of photon counting noise as you get fewer ...

41

This is a perspective effect. In essence, the second image is taken from a lower orbit which is closer to Earth, and the Earth only looks spherical because of the use of a fisheye lens that strongly distorts the edges of the image. This means that the field of view is a lot smaller. The Earth still looks like a circle on the page, though from close up the ...

41

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 detected. Even if the sensor is absorbing 95% of the light hitting it (ideally you want the sensor to absorb 100%) and the lenses reflect only 5% you still have 5% * ...

37

You can look up the camera settings behind these images. Here is the link to one of the raw images. The exposure time of the camera was 100ms. New Horizon's LORRI camera is a Ritchey-Chrétien telescope with a 20.8 cm diameter primary mirror and a focal length of 263 cm. That gives us approx. f12.6, which is a rather long i.e. fairly slow optical system (but ...

35

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 when the Earth has a high velocity relative to the camera - yet it is possible to get good images. What causes blur in the photo is not the speed of the object ...

32

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 the screen. Now let's displace the point source towards $D$ from the centre as shown below: The circular illumination also moves away from the centre but in ...

28

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 in front of an illuminated object, every point on the object emits light in every direction, which hits the screen at every point. You can imagine that the ...

26

In addition to the good answer of MSalters it is worth pointing out that individual photons arrive on the detector of the camera at different times. The way that cameras work is that they convert photons arriving into a signal that can be read out. No matter how high the fps rate there will be some point in time where one frame is finished and the new one ...

24

Are you aware that light consists of quanta (Sophia might have been a bit premature in her comment to say QM is not involved). Each photon captured by the camera is captured in one frame, for practical purposes. So the problem as we increase the FPS is that each frame is now based on fewer and fewer photons. This isn't just theory. We've done this ...

23

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. So you get a fuzzy image of the sun on the screen.

22

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 words, the optical axis). Similar lens flares are typically seen in images of the sun, for example in Apollo footage; moon hoax conspiracy theorists get all ...

22

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 infrared detector arrays like the HAWAII line of infrared arrays by TeleDyne. Typically, though somewhat less so as time goes on, the infrared arrays will have ...

22

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 semiconducting camera sensor normally used for capturing visible light, which relies on the photons interacting with electrons and electron-"holes" inside the ...

21

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. It only looks the right way up to you because you brain post-processes the retina image in the visual cortex. By looking with your eye at the image formed ...

20

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 speed of an object on the lens relative to the shutter speed of the camera. The shutter speed controls the camera's light sensor exposition time. For example: If ...

17

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 lens.. If the hole is too small diffraction becomes significant so that the final image becomes blurred. If the hole is too big the final image also becomes ...

16

The problem is that you are confusing light intensity with energy of a single photon. The photoelectric effect requires a certain energy per photon to work. But low light intensity just means fewer photons come - you can actually see the grain if the conditions are too dark: every pixel can get ~10 photons or less... and yet still, each photon that comes has ...

15

The Planck-Time is a little higher than $t_p=5\cdot 10^{-44} \, \text{sec}$ so the maximum frame rate allowed by quantum mechanics is less than $1 \, \text{frame}/t_p = 2\cdot 10^{43} \, \text{frames/sec}$.

15

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. Stacking medium length images provides some protection against faulty tracking. In the event of a tracking failure during a single long exposure there is ...

15

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 source is sharpest and only stack those. The technique is called Lucky Imaging and can deliver images as sharp as the Hubble Space telescope from ground-based ...

14

Just to add up on the previous answers, you can indeed see a few stars in the images but they are faint By adjusting the levels of the raw image, I obtain the following image where you can spot a few The adjustment I used is the level adjustment from gimp/photoshop/imageJ and I pulled the max level down. This effectively multiplies all pixel values by a ...

13

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 not reflect at all. Its position and size are based off the angle between you and the sun and the particular position of the elements in your lens. As for ...

12

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 the paper. Either you are relatively far away from the hole. Then it acts simply as a block. All rays from whatever is on the other side that do not go ...

10

I used a 8 million fps camera 25years ago - and the technology was old even then. I think purely electronic cameras can beat this by a factor of 10x today. Those cameras used a rotating hexagonal mirror and an arc of film, each frame behind an individual lens. As the mirror rotated it reflected the incoming rays onto each lens, and so each frame of film in ...

10

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 science of signal processing to detect signals much fainter than the background. Especially in IR astronomy.

10

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 experiment up to measure potential time-variation, there are quite a lot of advantages even for an unchanging source. Dynamic range: If your CCD has 12 bits, you ...

10

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 of the pinhole then it creates an inverted image of the object on the screen, how? An extended object can also be considered as a collection of infinite point ...

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