Optimal Exposure and Noise Calculator

[joseph.mcgee at sbcglobal.net]

Hi All,

Let me explain my reasoning for developing the optimal exposure 
calculator and noise calculator.  I started fairly recently in this A.P. 
hobby (mid 2019), and had no mentor. Most of the online resources seemed 
to provide information and suggestions that were geared toward imaging 
in very dark skies with more advanced equipment than a beginner would 
own.  The typical recommended exposure times I read about were on the 
order of a many minutes.

But when I was experimenting with and learning to use my gear, I 
typically did so in my own backyard (SQM 19.63).  I initially spent 
quite a few frustrating nights trying to find exposure settings that 
would produce a decent image.  As I acquired filters, I had to repeat 
the learning process.  Then when I had the opportunity to travel to a 
darker site 90 miles from my home, (SQM 21.65), I again had to repeat 
the learning process.  The difference in the exposure times at these two 
sites was pretty shocking to me.

I fully grasp that you all have considerable experience with A.P. but 
this tool is really not intended to provide benefit to folks that have 
such experience.  The target audience for this tool is the newcomer to 
this hobby (like me three years ago).  I would have been thrilled to 
have tool that says when I'm in my backyard shooting with gain at 100, 
and no filter, that my exposure time should only be around 45 seconds.

Now, back to the topic...

Warren,

You raised a suggestion that bias frames could be used to determine 
sensor read noise.  I must be missing some knowledge in this area. I 
just ran a test with my planetary camera (ASI-178), where I captured a 
set of bias frames incrementing the gain from 0 to 400 in steps of 50, 
with an exposure time 32us, (I believe that is the lower limit for the 
ASI-178).  I then used a tool that can assess noise in the image.  The 
noise measured in each image increased as the gain increased; so this 
did not match the downward trend I expected from the ZWO read-noise graph.

Perhaps the tool I used for noise assessment was not the best choice.

Can you explain further how I might be able to analyze bias frames to 
determine read noise?

Thanks