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exposure times in Scheduler
#1
How do you affect/set the exposure times in the scheduler?

is there a way to propagate those settings from the exposure calculator?

e.g. Exposure calculator says 10x10min exposures but scheduler says 100x1min exposures
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#2
Hello,

The Scheduler calculates the best exposure times based on the input you provided in the Imaging Project. The idea is that the Scheduler uses the selections in the Imaging Project as a guide, but makes choices based on the conditions at the time in order to maximize the SNR. The Exposure Calculator isn't constrained by the settings in the project (e.g. the project may force the sub exposure time) and this will not affect the Scheduler. This is so you can use the Exposure Calculator to explore different scenarios freely.

That said, if you open the Exposure Calculator via a right-click on the scheduled observation, the Exposure Calculator will open for the exact same time and conditions. This allows you to experiment with different settings. In doing this I see there are some possible pitfalls. Not all of the settings are transferred to the exposure calculator. In particular, the exposure goal information isn't transferred. So, for instance, if the Imaging Project has the exposure goals set for the "faint outer halo" then the Exposure Calculator needs to be set to the same. I also see that the weather settings are't always copied exactly either. So this may explain why the exposure calculator is giving you different information. I added the exposure calculator links on the Scheduler in the late stages and as an afterthought. I need to go back and make sure all of the settings are properly transferred. Keep in mind that under normal circumstances you would only use the Exposure Calculator in the planning stages.

There are other explanations for the difference as well. Perhaps you are reading the information in the Exposure Calculator table columns? The ideal exposure time specified there is something altogether different. It is only used as a starting point in the calculations. You can read about it on the help page of the Exposure Calculator.

If you have more questions, or more specifics, please free free to ask.
Clear skies,
Greg

SkyTools Developer
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#3
OK thanks, yes I read the help page of the exposure calculator.

I think something important for exposure calculations would be the max number of subs you want to have over the total integration time.

i.e. 1 min might be the "ideal" but if I know I don't want more than say 300 subs to stack (disk space, CPU, RAM limitations) then that should be taken into account.

I see it something like ST tells me I need ten hours per filter of total integration time, I tell ST the 300 subs max, ST scheduler picks the "best" exposure time (from my list of exposures time, if I have one) and used that in scheduling.

That's slightly different than forcing a say 120 sec exposure.

But in any case if I use the calculator to explore and find an exposure I want to use, it seems like the scheduler should use it, or at least the ability to enter it for use in the scheduler?

...

Haven't figured out multiple night schedules yet but will keep reading the excellent help file.
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#4
Hello,

Here's the thing: you presumably told it you that wanted either a total SNR of X, or a total exposure time of X. So it is going to find time in the schedule to reach that value of X. I you think about it, telling it not to use the total time available because you don't want so many sub exposures isn't really a very good solution. You won't get your SNR or Exposure goal that way. If you don't want to short exposures then setting a minimum exposure time is a much better way to handle it.

The Imaging System has settings for the allowed exposure times. You could set the minimum exposure time for the imaging system to 2 minutes. If that is not a good solution for some reason, would it help if I added an minimum sub exposure time specification to the project?

This is a pretty big can or worms that you want to open here. If we start micro managing the Scheduler, then we will not reap the benefits of the calculations that it makes. After all, it presumably chose one minute subs for a good reason. That said, I am considering some limited schedule editing abilities. But these would be designed for special purposes, rather than be kludges. A kludge should not be necessary. A kludge means that either the user has missed the better way to do it, or I need to add a full (non kludgey) feature.
Clear skies,
Greg

SkyTools Developer
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#5
I'm not sure I was clear on the difference between the Exposure Calculator and the Scheduler when it came to sub exposure times. Unless something is broken they should return same result. But there are many inputs that must all be identical, and it can be tricky to ensure that the Exposure Calculator is set exactly the same.

I would trust the Scheduler over the Exposure Calculator because it has all of the information.
Clear skies,
Greg

SkyTools Developer
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#6
OK thanks. Some questions on the exposure calculations.

Because of the small pixel size of the ASI1600, even with a Focal Reducer my image scale is over sampling at .4 arcsec/pix. Target selection says optimum binning for all targets is bin 1.

Exposure calculator says I need 11:20 to reach SNR of 50, with Ha at bin 1. Changing (only the bin) to 2 it says I only need 160min. Is that correct? Because of seeing would my effective resolution be similar with both binnings?

Interesting that changing the gain doesn't seem to affect anything (sub exposure or total integration time to reach 50 SNR) I can see the gain not affecting the total integration time, but shouldn't the sub exposure become shorter?

Without opening a can 'o worms ;0) does the exposure calculation consider dynamic range and saturation of stars? I've seen it say saturated when you tell it to image during the day, but never just from increased gain or exposure time.
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