2018-09-27, 01:59 AM
The "ideal" exposure time is often not the same as the exposure time that delivers the most SNR. The ideal exposure time is computed via a fairly well known formula. But this formula is limited by real world considerations that I does not include. What SkyTools does is to look at a fixed period of time. It tries different sub exposure times and takes the one that delivers the highest SNR, and this is often not the same as the ideal time. Also, you may have set up your Imaging System with a minimum exposure time of one minute. In that case, SkyTools will use 1 minute subs even if something less would increase the SNR.
There is a section in the Technical Reference of the Help about ideal sub exposure times, how they are calculated, and what the limitations are in real world applications.
OK, doing more fiddling around ... the Exposure Calculator seems to be oriented around "what can I accomplish with the viewing session tonight", either "what's the highest SNR image I can take if I use the entire period for the IQ requested" or "how long will it take to get to the SNR requested given the period that the IQ is at the level requested" ... OK, got it ...
For multi-night it looks like a combination of Imaging Project dialog plus the scheduling window is what I need ... so from the attached project of M100, I can see ...
From the Imaging Project dialog, for an SNR of 20 with this object, IQ of A it will take me 22.1hr of imaging to get to where I want to be [yes?]
From the Scheduler, on the date that this is selected for the period selected ST4 is telling me that I need to take 51x1 lights of this object (91min total runtime, 51min total integration time) [yes?]. The lower listbox is telling me that this evening will complete 17% of my total integration time, and I will have an SNR for this evening of 3 for this light once it's been stacked [yes?]
Based on this information, I do a run that evening, and record the results the next morning in my observation log for the project ...
... note that even though I've set the exposure count and time in the "Edit Observation" dialog as 51x1, in the Imaging project dialog it's seeing this as 1 acceptable image with a total SNR of 0, completion 0% with a total time spent of 51min ... in the Observations section of the Imaging Project it reflects that as well, 51x1 exposures but no images ... is the program expecting some additional info?
I progress to the next day in the series, the 30th, but the schedule here doesn't recognize the exposures that I did on the 29th ... what should I do to cause it to recognize the previous observation period on the 29th and continue the series?
Also, let's assume that we figure out the progression and each day I do an additional 51x1 lights for another 17% ... that means that when we reach 100% we will have completed a total of 300min of exposures, or 5hr ... but that's much shorter than the Imaging Project dialog which tells me I have 22.1hr of exposures to do ... what could cause this?
Soldiering onward!
There is a section in the Technical Reference of the Help about ideal sub exposure times, how they are calculated, and what the limitations are in real world applications.
OK, doing more fiddling around ... the Exposure Calculator seems to be oriented around "what can I accomplish with the viewing session tonight", either "what's the highest SNR image I can take if I use the entire period for the IQ requested" or "how long will it take to get to the SNR requested given the period that the IQ is at the level requested" ... OK, got it ...
For multi-night it looks like a combination of Imaging Project dialog plus the scheduling window is what I need ... so from the attached project of M100, I can see ...
From the Imaging Project dialog, for an SNR of 20 with this object, IQ of A it will take me 22.1hr of imaging to get to where I want to be [yes?]
From the Scheduler, on the date that this is selected for the period selected ST4 is telling me that I need to take 51x1 lights of this object (91min total runtime, 51min total integration time) [yes?]. The lower listbox is telling me that this evening will complete 17% of my total integration time, and I will have an SNR for this evening of 3 for this light once it's been stacked [yes?]
Based on this information, I do a run that evening, and record the results the next morning in my observation log for the project ...
... note that even though I've set the exposure count and time in the "Edit Observation" dialog as 51x1, in the Imaging project dialog it's seeing this as 1 acceptable image with a total SNR of 0, completion 0% with a total time spent of 51min ... in the Observations section of the Imaging Project it reflects that as well, 51x1 exposures but no images ... is the program expecting some additional info?
I progress to the next day in the series, the 30th, but the schedule here doesn't recognize the exposures that I did on the 29th ... what should I do to cause it to recognize the previous observation period on the 29th and continue the series?
Also, let's assume that we figure out the progression and each day I do an additional 51x1 lights for another 17% ... that means that when we reach 100% we will have completed a total of 300min of exposures, or 5hr ... but that's much shorter than the Imaging Project dialog which tells me I have 22.1hr of exposures to do ... what could cause this?
Soldiering onward!