DATE-OBS – date of observation in the ISO standard 8601 format (Y2K compliant FITS): CCYY-MM-DDThh:mm:ss.sss. The Universal time at the start of the exposure is used. Note: the alternate format using DATE-OBS and TIME-OBS is not written, but MaxIm DL will correctly interpret it when read. The time is written to 10 ms resolution. The default behavior is to report the start of observation time, but individual camera drivers can change this. As of Version 6.24 the DL Imaging driver sets the time to exposure midpoint.
So there is NO standardized point in time specified for DATE-OBS.
My camera is a QHY model. Do I understand correctly then that the QHY camera driver writes DATE-OBS to the header, or does SGP do that itself? If the former, I’ll need to check with them on what time this represents.
However, if it’s the latter, does SGP document this somewhere, or could somebody from SGP please verify? Thanks!
I was having a related issue just the other day and Ken (SGP founder) says that they write the start time provided by the camera or “guess” at the time if no time is provided. Note that the time is only to the nearest second in spite of the precision of the format. I don’t know what “guess” means as Ken has not gotten back to me with an explanation. I have the QHY 268M.
To be fair, you never asked that question of me? I seem to be the last reply on your thread here…
That said, it’s no problem explaining… The notion of a guess here means that SGPro can only know the time it requested your camera start integrating and not the exact time that camera actually started integrating. SGPro cannot know the actual time the camera began its integrarion, but this guess will be sufficient for most. This is why we always favor the camera’s onboard time (when it provides it) as opposed to the integration request time. It is supposed to be more precise, but in the issue you describe it is not. This can be fixed within the QHY ASCOM driver… seems like there is some rounding going on there somewhere…
I was wondering why you hadn’t responded as you are always very prompt. I figured you might be busy but I must have forgotten to hit reply when I replied to the thread asking for an explanation. Sorry! Thanks for the explanation. Using system time for the “guess” then. Good enough!