Sun, 06/06/2021 - 10:06
I would like to know if dark frame scaling is possibile with new CMOS cameras in the event of a camera that shows zero amp glow such as the QHY600 or QHY268. Since the electronics of these new cameras are also very stable I wonder whether one could even skip master frames and just subtract one single dark frame of corresponding exposure or one single scalable dark after subtracting a single bias. Of course gain, offset and temperature match the ones of the calibrating frames.
Gianluca
Why don't you try it on photometric standard fields and let us know what happens?
Roy
My previous comment was somewhat peremptory, but in defence, was prompted by real curiosity in what was proposed.
In view of that, it is only fair that I describe an experiment of my own, not exactly like the proposed procedures, but I think not unrelated because of the outcome.
DSLR photometry was performed from a fixed tripod through a 200mm lens on a target field with 6 standard stars. Each of them in turn was designated the target, with the other five used as comp stars for ensemble photometry. Exposures were 15 seconds at ISO 400, and 10 exposures were taken in each set. 15 darks were taken, as were 60 carefully taken flats. Each transformed magnitude was the average of measurements on 10 images.
Three sets of results were calculated: 1. Photometry on uncallibrated images; 2. Photometry on images callibrated with darks only; and 3. Photometry on images callibrated with darks and flats. Errors were calculated as measured magnitude minus catalogue magnitude.
Photometry on images callibrated with darks only was mixed in terms of accuracy, with some results better than those from uncallibrated images, and some worse, and the differences between callibrated and uncallibrated images were not very much. However, when callibration with darks and flats was done, the accuracy improved dramatically for V magnitude measurements (errors were much smaller).
Bear in mind that the exposure were only 15 seconds. With other equipment and procedures and longer exposures, the results may of course be different.
However, in view of your question, I thought the above relevant, which showed that good flats were critical for best results, whereas darks alone, under the conditions described, were not as critical.
Roy
I am unable to…
Hi Roy,
I am unable to do photometry at the moment as I am waiting my new SDSS filters. It will take a few months as the manufacturer has a backlog. I also think that flats are of the most importance. As regards darks given the new cameras has very stable electronics I think that just a single dark subtraction together with a master flat will probably do. I will of course do the test but it will take a few months.
Gianluca
Hi Roy,
I am unable to do photometry at the moment as I am waiting my new SDSS filters. It will take a few months as the manufacturer has a backlog. I also think that flats are of the most importance. As regards darks given the new cameras have very stable electronics I think that just a single dark subtraction together with a master flat will probably do. I will of course do the test but it will take a few months.
Gianluca
I hope your…
Hi Gianluca,
I hope your vendor clears the backlog soon.
Our cameras are of course very different, my DSLR being very noisy. So I was surprised that darks alone (I averaged 15 frames to make the master) gave mixed results and made very little difference.
Roy