Hi, I know that if you are imaging using the HSP read mode, that your darks need to be in HSP as well (and time and temperature matched). What if you change the minimum HSP "Stacking Sub-Exposure" setting in the DL Config tab from 2 sec to 30 sec? For a 90 second HSP exposure, instead of 16 stacked sub-exposures of around 5.6 seconds each, you would have 3 subexposures of 30seconds each. If I make such a change, do I need to do new HSP Darks with the stacking subexposure minimum also matched? Thanks for the input, Best Mark
Yes, you must match: Temperature Exposure Readout Mode Target Subexposure If you change the Target Subexposure then you'll get a different number of subexposures stacked with different exposure times. So it's going to be very different.
Doug, in the FWIW category, since the fits header doesn't show what the dark frame HSP subexposure was, if you are unsure about what the HSP subexposure setting was, but know that it was one of a few settings that you use, use pixel math to subtract a single dark that you are sure about from the unknown one (same overall dark exposure and temp and binning of course). If you end up with a significant difference image, then you'll know the unknown dark image doesn't have the same subexposure setting. I just tried that on a dark that I thought might not have had the subexposure setting changed from 2 to 30sec. I compared it to a known 30sec sub and got a significant signal, indicating it was actually one of my 2 sec subs. Subtracting known 30sec subs from each other and known 2 sec subs from each other yielded a difference image that was of very low signal with some cosmic ray hits visible. Obvious to most I guess but interesting. I suppose what I'm seeing is the extra read noise from 16 subexposures stacked vs. 3 subexposures stacked when comparing the 2 sec and 30 sec subs in an overall 90 second dark. Best, Mark
You'll definitely see a shift in the bias level (average image background) if the number of subexposures is different. We'll look into adding additional information into the FITS header. In the meantime, I expect most people will settle on a target exposure that works well with their setup. Unless you're shooting a target with extremely bright stars in it (e.g. Trapezium) there's probably a setting that works well in most situations.
Yes, I'm sure most won't change it often. I'm still experimenting with it in connection with finding my maximum acceptable unguided imaging duration (I'm using a 4200mm FL scope). For 60-120 second unguided exposures, it may be that I want to set the subexposure time to something higher than I would if I was using 5-15 minute guided exposures (to reduce the number of internal chip readouts of really short subs). It may not matter, but minimizing the pattern noise is a good goal. Are you seeing any advantage to using slightly warmer cooler temperatures? My routine would be -5C in the summer and -10/15 in the winter. Last night I saw some residual image in the darks that went away once I warmed up and re-cooled the camera. Best, Mark [Edit, I am using more dithering than I used to based on our conversation. I think that does help]
In general, RBI does tend to be worse at colder temperatures. (That goes for all silicon detectors.) I haven't experimented with that myself.
Hi Doug, Have you thought further about adding a line in the FITS header that shows the HSP subexposure setting? I usually use one of a couple of different ones, but it would be helpful long term to have that information imbedded. I sometimes forget to catalog the files in folders with that info. Hope all is well, Best regards, Mark
Hi, thought I'd ping again about the utility of having the FITS file capture the HSP stacking subexposure duration. It really would be nice information to have for calibration purposes as well as general reference later on when working on setting up an exposure plan for an object. Thanks for considering it, Best regards, Mark
It's already been added, and will be released with the next minor update. Assuming all goes well it should be released in December.
