A lot of noise in night sky photos

Okay, this has already been said but I feel its worth saying again. Noise increases in dark areas of an image due to stray photons that the human eye doesn't see.
Err .... !

No.

Actually, thats wrong.

There are two major variants of noise:

1. Dark current, i.e. noise because of electron movements from the temperature of the sensor, even if there is no signal at all on the sensor. This type of noise constantly happends. That means: long exposures will have more of it. You can get rid of this variant of noise by cooling the sensor, the more the better. Astronomers might use sensors cooled to a few degrees above absolute zero, reducing the dark current to neglible values. But since that is no option on conventional cameras, we use "long exposure noise reduction" instead. In that mode, the camera will take a second frame to estimate current noise levels (since this depends upon temperature, they wont stay the same).

2. Photon noise. This is noise because of the random distribution of photons. This matters more if you use high ISO, because ISOs above the base ISO of your sensor, you will amplify the signal from the sensor, i.e. get your output signal from less photons total. This kind of noise is why larger sensors with low base ISO can capute more color information than smaller ones with high base ISO.
 
Okay, this has already been said but I feel its worth saying again. Noise increases in dark areas of an image due to stray photons that the human eye doesn't see.
Err .... !

No.

Actually, thats wrong.

There are two major variants of noise:

1. Dark current, i.e. noise because of electron movements from the temperature of the sensor, even if there is no signal at all on the sensor. This type of noise constantly happends. That means: long exposures will have more of it. You can get rid of this variant of noise by cooling the sensor, the more the better. Astronomers might use sensors cooled to a few degrees above absolute zero, reducing the dark current to neglible values. But since that is no option on conventional cameras, we use "long exposure noise reduction" instead. In that mode, the camera will take a second frame to estimate current noise levels (since this depends upon temperature, they wont stay the same).

2. Photon noise. This is noise because of the random distribution of photons. This matters more if you use high ISO, because ISOs above the base ISO of your sensor, you will amplify the signal from the sensor, i.e. get your output signal from less photons total. This kind of noise is why larger sensors with low base ISO can capute more color information than smaller ones with high base ISO.

Well sure I was simplifying, but I'm not exactly wrong.. Photon noise is increased by a long exposure as well due to the increase in time that the sensor is exposed to light in general causing more "stray photons" to become exposed. So sure photon's play less of a role in long exposure noise than dark current but it is still more present than it would be at 1/1000th of a second.

It's just alot easier to say "some extra photons hit your sensor bro" than it is to describe that heat interference is causing a mechanical malfunction.
 

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