Optimal Exposure and Noise Calculator

[Warren]

Hey Joseph, you may inadvertently be getting some light into your bias
frames. Make sure you cap the camera like you’d do for dark frames.

Here’s a more explicit, complete process for measuring read noise from bias
images. I don’t have access to an astro camera at the moment (I’m snowed in
at Lake Tahoe, boo hoo) to verify this process, but I can try it myself in
a couple days.

http://astro.physics.uiowa.edu/~kaaret/2013f_29c137/Lab03_noise.html#:~:text=The%20read%20noise%20of%20the,removing%20hot%20and%20dead%20pixels
).

In regards to subexposure length, I’m not personally against the
calculator, but maybe it should have a disclaimer. I think it’s true that
almost everyone using recent CMOS cameras should just use, say, two minutes
by default. This consistency really simplifies workflow.

If you have trouble with tracking, periodic error, tracking, fast high
clouds, wind gusts, polar alignment, etc. then you can switch to 30- or
60-second subs with almost no effect other than using more disk space and
more CPU time.

There may be people using older CCD cameras with KStars / Ekos though!

- W

On Sat, Mar 4, 2023 at 10:38 PM Wolfgang Reissenberger <
sterne-jaeger at openfuture.de> wrote:

> Joseph,
> I’m not sure what type of function we are talking here. Is your intention
> to calculate the optimal exposure time for a single frame or for the
> target? If its the first one, I have the same questions as Hy. For the
> latter, I’m happy to learn more about it.
>
> Wolfgang
> —
> Wolfgang Reissenberger
>
> www.sterne-jaeger.de
> TSA-120 + FSQ-85 + epsilon-160 | Avalon Linear + M-zero | ASI 1600mm pro +
> 6200mm pro
>
> Am 05.03.2023 um 06:06 schrieb 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
>
>
>
>
>
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