Why is it enough for a person to see the stars to look at them, while a camera needs a long exposure?

Why is it enough for a person to see the stars to look at them, while a camera needs a long exposure?

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answers (3)

Answer 1
January, 2021

Not quite the answer to the question asked, rather an addition. Currently, not every camera needs a slow shutter speed. And what is most important, we are not talking about professional highly specialized equipment, which is used for scientific purposes or specifically for astrophotography (cameras converted for higher sensitivity), but about ordinary cameras and cameras.

For example, video-oriented cameras sony a7s i / ii. Yes, these are very expensive cameras. But they remain "just" cameras, besides the sensors in these cameras have gone further, they not only "see" well at night like people, they "see" even better.

As for contrast, there are already special codecs that extend the dynamic range, but they are used only in movie cameras. Although there are budget options like black magic.

Answer 2
January, 2021

Shooting stars is not an easy process, now this type of shooting is singled out as a separate genre - "astrophotography".

Seeing stars and photographing stars are two big differences, as even the brightest stars are dim in brightness. But we can see them easily!

This is due to the fact that our eyes, like the eyes of some animals, have a physiological property donated by nature itself. It can simultaneously see quite bright objects like the Moon and such faint objects like stars.

And the electronic matrices of modern cameras do not have this property.

Shooting the night sky is not the only situation where what we see is different from what we get in the frame.

Take any high-contrast landscape scenes: bright rays of the sun making their way through tree trunks of an autumn forest or just a very bright sky in contrast with a dark forest.

Too much contrast between some parts of the frame leads to the fact that either light areas are worked out, and details in the shadows are lost, or, conversely, bright areas come out overexposed in the image.

Such situations clearly show the difference in the dynamic range of the eye and the camera.

Our eyes are capable of looking around the scene and dynamically adapting depending on the object, while the camera records a single still image. Many consider this to be the main advantage of the eye over the camera.

If you want more information, you can read this article.

Answer 3
January, 2021

The photoreceptors of the "stick" are responsible for vision at night, in extremely low light conditions.

About them on the wiki:

The sticks are sensitive to light due to the presence of a specific pigment - rhodopsin (or visual purple). Under the influence of light, a series of very rapid transformations and discoloration of the visual pigment occur. The stick's sensitivity is sufficient to register even 2-3 photons hitting.

The sensitivity of cameras is lower. Therefore, the camera is forced to accumulate the signal.

Not a bad article on a set of problems when designing a camera matrix:

www.ferra.ru

the sensitivity is determined by the photocurrent of the CCD element, that is, the charge accumulated by the potential well. The amount of accumulated charge depends on a number of parameters.

For example, the larger the fill factor of the CCD element, the higher the fraction of photons that can be absorbed to create charge carriers. That is why, with increasing matrix resolution, one of the main tasks for developers is to ensure the maximum possible area of ​​the photosensitive area. To do this, the dimensions of the strapping (transfer electrodes, drainage and buffer columns) should be reduced in proportion to the increase in the number of pixels.

CCD material must meet a number of requirements - have a minimum reflectance and a maximum absorption coefficient in relation to photons with the required wavelength and at the same time reflect and not absorb photons from other regions of the spectrum.

(filters are used for the solution)

Along with the area of ​​the photosensitive area and the quantum efficiency, the sensitivity threshold - the value of the minimum light signal that can be detected by the CCD element - affects the ability of a pixel to register photons (the weaker the signal, the higher the sensitivity threshold). The dark current, which appears in the CCD element at the moment the potential is applied to the electrode, under which a potential well is created, has a negative effect on the sensitivity threshold.

No less destructive than dark current, thermal noise affects the sensitivity threshold. This phenomenon is caused by the chaotic movement of charge carriers in the thickness of the semiconductor, which does not stop even when the potential supplied to the electrode is turned off.

But, in principle, supersensitive receivers already exist in everyday life. A video camera (that is, shooting like an eye, instantly) with a sensitivity that allows you to shoot a starry sky:

https://www.youtube.com/embed/yBvKGnr3B1U?wmode=opaque

and the corresponding price - one and a half million rubles)

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