Reference of timestamp

Using SharpCap for other Astro Imaging such as all sky cameras and meteor detection
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michastro
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Reference of timestamp

Post by michastro » Sun Jan 26, 2020 11:57 am

Hello,
I use SharpCap for occultations, and I have to make quite long exposure time for faint stars. I use the inserted timestamp, but I would like to know if the timestamp inserted is the beginning, middle or end of exposures?? Of course logicaly it should be middle of exposure, but...
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Michel Meunier
http://team-janus.astrosurf.com/index.p ... janus-sud/

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Re: Reference of timestamp

Post by admin » Sun Jan 26, 2020 5:38 pm

Hi Michel,

Sadly the answer to this question is 'it depends'. Assuming that you are using a normal camera (not a QHY GPS camera), then the timestamp is usually the time at which SharpCap received the frame from the camera, which will be a point in time after the end of the frame.

Unfortunately SharpCap has no idea how long it takes for the image to be transferred from the camera to the computer and then handed over to SharpCap from the camera manufacturers code. Typically four USB3 CMOS cameras, the delay is small (much less than a second). For CCD cameras or USB2 CMOS cameras being run at long exposures the download time to the computer may be several seconds.

The exception to the rule about the timestamp being after the end of the frame is if you are capturing to FITS format in a recent version of SharpCap 3.2. In those circumstances, SharpCap will attempt to estimate the start time of the frame by subtracting the exposure duration from the time that it receives the frame and putting that value in the DATE-OBS header of the FITS files. This change can be found in SharpCap version 3.2.6131 and newer versions.

Hope this helps, Robin

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