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ISO - exposure - temp relation

PostPosted: Fri Jul 05, 2019 8:56 pm
by AstroChris
Hi folks.

I just had a session on M27 with my dslr Olympus e510. It turned out that my subs nearly had no information above noise-level in the red channel. I then asked myself (and you)

A) what are the correlations between the variables temp/iso/exposure time.

My second question was:

B) why have i no signal above noise-level in red but signal in the G and B? Are red pixels more sensitive to temp-related iso noise?
B.1) -> are long exposed darks therefore "red"?

I searched some images and compared the three colour layers in light frames and in darks. I used only single subs and no stakked images as i want to investigate what the dslr can see.

Result 1) The rise of noise in the red channel is highly related to temp and iso is huge. At 8°C there is "little" noise in 25° there is just too much noise for signal to come "through'.

Conclusion 1) At a given temperature there is without any other helping tools no way to take images. Till now it seems that temps over 25° with iso 800 and 120sec seem like a border for my old cam. This might vary from chip to chip but for every chip there must be a border where noise rises above signal.
The red noise can be caused by light pollution or by temp-iso noise.

Result 2) indeed in the darks (taken in a dark bag at night) the red channel is more nosey than the other two channels. This indicates that the red channel is more temperature sensitive then the G and B. Red noise in the darks is caused by temp-iso-noise. Wether this is a specific chip issue or a general thing must be sorted out.

I will post some images for comparison.

Greetings
Chris

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Re: ISO - exposure - temp relation

PostPosted: Fri Jul 05, 2019 8:59 pm
by AstroChris
Light iso 800
120 second sub
Both images in red channel


Temp 25C on m27 or temp 5C on m13
export_light_frame_red.jpg
M13_herkules_iso800_120sec_8c_R.jpg


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Re: ISO - exposure - temp relation

PostPosted: Fri Jul 05, 2019 9:00 pm
by AstroChris
Dark
120 sec subs
Iso 800
Both images in red channel


Again 5c and 25c
Dark_M27_120sec_iso800_25C_R.jpg
Dark_M13_120sec_iso800_8C_R.jpg


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Re: ISO - exposure - temp relation

PostPosted: Fri Jul 05, 2019 9:02 pm
by AstroChris
Compare iso 800 120 sec subs at 25°

R and G
Dark_M27_120sec_iso800_25C_R.jpg
Dark_M27_120sec_iso800_25C_G.jpg


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