When I was taking a course on CCD Photometry with the AAVSO this past February I asked the instructor how he would solve my problem having an uncooled camera. I hadn't yet come up with my idea of a Temperature Logger so I was at a loss of how to capture a 2.5 hour long sequence of a short-period variable star. He suggested taking two lights and then one dark. This is not difficult for users of CCD cameras because some (many?) of them have mechanical shutters. I don't have that option with a CMOS camera, so another option was to run outside in the freezing weather every 3 minutes to place a lens cap over the objective and then push a button to collect one dark, and then run back inside to warm up and take 2 light frames using the remote connection to the telescope, repeat again and again and again. The last option that he suggested was to capture darks before and after the 2.5 hour sequence and average the darks together in a master dark. That's what I did.
Back then I had a manual filter wheel with a dark filter in the carousel. In the cold temperatures the wheel was difficult to turn. Months later I purchased an EFW. Much, much better but still I've found that it is good to refocus after every turn of the wheel. I don't yet have a powered focuser motor but plan on it soon. Of course it would be great to be able to script all of this. I know that this is possible with SGP.
I've attached the report that I generated with a program called VPhot. It shows the light curve of the variable star YZ Boo. Over the course of 2.5 hours it dimmed 0.5 magnitudes. These are 100-second exposures at low gain. Calibration frames were applied to each frame but no stacking. The reason for the low gain is to capture a wide range of comparison stars at high enough SNR to be statistically significant. You can't achieve that at higher gains. There is a graph called Sky Glow. The quarter moon was at the meridian when I began and was about to set when I finished. These were taken with a "V" photometric filter ("V" = Visual = wideband green.)
Somewhere to share your expertise in using SharpCap
- YZ Boo VPhot Time Series.jpg (192.17 KiB) Viewed 274 times
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