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Starting CMOS photometry

Calculad
Affiliation
British Astronomical Association, Variable Star Section (BAA-VSS)
Fri, 10/20/2023 - 19:05

I finally have my system ready for CMOS photometry.

StellaMira refractor, 90mm ED triplet, FL 600mm

ZWO – AISI 1600MM Pro (cooled) camera

Baader Bessel Photometric B&V filters

Controlled by ASIAIR Plus

 

Now I am trying to find my way through the labyrinth of settings available for CMOS imaging/photometry.

I'm really just looking for some simple starting points to my settings.

I'm thinking of optimum or at least somewhere to start.

The following are of relevance to darks, flats, bias, and dark flats.

Gain, Temperature(cooling), Offset, Binning,

I was trying prepare some of these on the cloudy nights we are stuck in.

I have to select values that will match my lights (science images)

I'm guessing there isn't a simple answer but any starting points would be helpful.

 

I took some test images of M11 and with 30s unguided exposures and could "see" stars down to 13th mag.

I am in the middle of the brilliant VPhot course which really starts with the assumption of calibrated images.

That's the step I need to go back to.

Thanks

Kevin

arx
Affiliation
Variable Stars South (VSS)
Sat, 10/21/2023 - 22:07
Kevin,

I started a few…

Kevin,

I started a few years ago with virtually identical equipment, including the ASI1600MM camera. Because it is a 12 bit camera and has a lower QE than some others, I found that precision is optimised if the magnitudes of comparison and check stars are as close as possible to the magnitude of the variable. My targets are contact or near contact EBs and hence usually have periods of less than a day, sometimes just a few hours. I take time series with exposures of 60-90 seconds when possible. Exposures may be shorter for brighter stars. I set the gain to give me the longest exposure possible within the above range. Try starting with zero gain. I find it useful to know the gain settings that give system gains of 1, 2, 3, 4 and 5 e-/ADU. For fainter stars I prefer to set the gain higher than zero, to achieve sufficient peak ADUs.

I use an offset of 50, but experiment to make sure that is high enough for you. I take images unbinned. The reason is that in ZWO ASI cameras binning averages the ADUs of binned pixels. A pixel may be saturated and you could not tell.

I set the temperature to -10 deg C.

The above works for me. Others may have different strategies.

Roy