Exposure Calculator

[Warren]

I think a fundamental problem with this approach is that it tells you the
*minimum* acceptable exposure duration, which is long enough for some other
noise source (likely skyglow) to greatly exceed your sensor’s read noise.

This is useful information, but mostly when you’re shooting from a Bortle
1-2, where your sensor’s read noise is potentially the limiting noise
source — where 60 minute narrowband subs make sense.

For folks in urban and suburban environments, with modern low-noise
cameras, any realistic exposure duration (e.g. 60-300 seconds) is
sufficient for skyglow shot noise to greatly exceed sensor read noise.

On Wed, May 17, 2023 at 10:55 PM Hy Murveit <murveit at gmail.com> wrote:

> Joseph,
>
> Thanks so much for getting the exposure calculator up and running in
> KStars. Impressive accomplishment!
>
> I just tried using it, and have some questions/comments I was hoping you
> could address.
>
> Here's a screenshot, with questions below:
> [image: Screenshot 2023-05-17 at 10.13.06 PM.png]
>
>    - I think I filled in the boxes appropriately above, though not sure,
>    please let me know. I tried these values: sky quality 19 (about what I've
>    measured at my house), f/8 reflector, full bandwidth (300nm), my ZWO
>    ASI1600mm camera at gain 75 (I assume it wants the gain I use for the 1600,
>    but I tried other values too), 20 total hours of exposure time desired,
>    default noise increase of 5%. It seems to be telling me to take 5956 images
>    each 12.09 seconds long, which is obviously not a good answer. Am I doing
>    something wrong?
>    - Not sure what Stack Time, Stack Noise, and Ratio mean. Are shot
>    noise and total noise in electrons? (Need tooltips to help)
>    - I was able to get it to give me a reasonable exposure time (e.g.
>    about a 2-minutes) if I set Noise Increase % to 0.4, but I really didn't
>    know what to put in there, and so used the default was 5%. Do you know, is
>    5% a good default for the noise increase? Can we give more guidance on what
>    noise increase people should start with?
>    - The tool needs better tooltips for pretty much each value that needs
>    to be entered.  Most  tooltips say "An implementation of Dr Robin Glover's
>    exposure calculation." We can give credit elsewhere (e.g. usually done in
>    "About KStars"), but the tooltips should be informative. For instance, is
>    gain the actual gain values one enters for the camera, or do you mean
>    something like quantum efficiency? Assuming it's the value entered to the
>    camera's driver, you should say that "Gain value used for your camera".
>    Filter Bandwidth should include units (e.g. nm in this case.).
>    - Don't need 3 decimal places for Sky Quality (make it one or two
>    decimals). Ditto for focal ratio.
>    - Is there some documentation on use somewhere? E.g. can a section be
>    added to the handbook? Also, please start a forum thread describing this
>    new tool and how you recommend users use it.
>
> Thanks again,
> Hy
>
>
>
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