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Looking at ASI1600 Pro Bias and Dark Flats


paul
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Thinking what to do about Bias (dark Flats) and prompted by an Adam Block tutorial I decided to have a look at what they look like for the 1600. I captured 30 darks at 0.01, 0.1,0.2,0.5,1,5 and 10 seconds at gains 0,139 and 200 (camera at -15 C). 

 

Looking at the data I decided to concentrate on 0.01, 0.1 and 10 sec and use Pixelmath on the stacked images to do comparisons.

 

At Gain 0 it is possible to see the Fixed pattern noise (if stretched):

 

image.png.f14a9174a7fc73efd173ab7742a24783.png

 

The banding variance at Exp 0.01s is small (K varied <> 3 parts in 10k) with average K being about 0.0118. At Exp 0.1s K is approx. 0.0119 and at Exp 10s K is approx. 0.0119.

 

If you subtract the 0.01s from 10 s exposure the average result is around K0.00007. The delta image shows no evidence of amp glow (even with NB my flats aren't normally longer than 10 seconds so that is good news):

image.png.36145622db23c8131c47b5404556b0a9.png

But it shows more hot pixels developing.

 

I will run the test again on another night to see if these results are repeatable. If they are then I can construct a library of Bias/Dark flats. As long as the banding stays consistent even small variations from session to session in the bias values can be ignored - Flats have a typical K value of 0.5 so small variation around K0.0005 should have little impact in the profile.

 

My data for gains 139 and 200 seems suspect, there is evidence of faint vignetting and the FPN has disappeared, suggesting that even though it is a very small signal I think I have some light leaking in. Another reason to redo the test.

 

Edited by paul
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