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Interpreting ISO test results

Beginner Astrophotography DSLR Imaging
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#1 Galactus

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Posted 06 March 2021 - 12:53 PM

I am trying to figure out the optimal ISO with my Nikon D300s full spectrum mod. I took 20 second exposures at iso 200, 400, 800, 1600, and 3200. I was half expecting to see read noise decrease with the increase in iso assuming my camera is iso variant. The opposite seems to be the case here as the noise increases with along with iso. Now, I am not entirely sure I am running this test correctly as I took the exposures and auto-stretched the raw files in PI, is this an appropriate way to run this test? 

 

Also, is there a way to distinguish read noise from shot noise just by looking? I have a hunch that I should explore the ccd parameters script in PI some more but I am unsure what values I'd be looking for. 

 

I have imaged a few times between iso 800-1600 with gratifying results, though my alt-az is the primary limiting factor (G11 arrives in a few weeks!) but I would still like to get closer to optimal setting for this camera.

 

DSO only so far, so I chose M101 for the tests, through celestron nexstar 8se with .63 focal reducer. I think my back focus may need to be adjusted since getting it camera modified, but I haven't had an imaging session yet so well see, tonight is looking promising. 

 

I apologize for not posting the pictures here but they wouldn't fit. In the drop box folder, are the stretched images and the raw files incase those are any use.

https://www.dropbox....LN4v0lgJFa?dl=0

 

To sum up, I'm trying to get a better idea of optimal ISO, and am unsure how to interpret my test images, any insight here would be greatly appreciated!

 

Kind regards,




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