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I’m using GStar camera with SkyWatcher 150x 750 refractor from very light polluted Sydney suburb backyard. The camera uses ½” Sony Ex view chip with pixel size 8.6x8.3um. AD converter is 8 bit only and frequency response is within 5% linear from 480 620nm. But it is very sensitive - 0.0001 lux at f1.4. Images are taken as 2.56 seconds FITS exposures stacked on the fly with dark (bias corrected) subtracted from each exposure by capture software. Darks are generated for every 1degre C of temperatures drop by stacking 250 exposures, bias subtracted and scaled 0.004. I do not use Flats as it used to generate more problems the it solved. The 25 or 50 exposures make my “Sub”. Three to four such subs are taken of each object of interest and then processed in Maxim DL. Firstly one of the subs is plate solved with PinPoint (to make sure that I did got stars I intended), then Fits header is modified with object name and exposure time and filter used. Capture software I’m using doesn’t do this automatically. Then subs are flipped or mirrored to have North up and right way around (helps me with orientation in the planetarium software) and bad pixels removed (by using bad pixel map) I’m aware that if I use Maxim for capturing, I could have images plate solved and facing right way around in first place, but I would also have up to 200 FITS files for every object I image. Then I align and stack Subs. Except of screen stretch I do not do any other processing. Then I plate solve final image. The residual is between 0.2 and 0.6-arc/ sec., depending on seeing and general conditions that night.
I have a GSC2, Tyco2 and UCAC2 catalogues installed but use UCAC2 most of the times. I can do photometry on stars from Mag about 7 to about 14. Any stars brighter then this are saturated and fainter one have S/N ratio too low. Although I can see to mag 18 on occasions.
I imagine to about 30 deg or less from zenith otherwise the sky glow from surrounding suburbs become too bad. For photometry I use only about 1/3 of central image area. I believe that PinPoint automatically compensates for atmospheric extinction, but I better check it up.
Any comments as what I’m doing wrong appreciated.
How do you do “differential photometry” ?
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