Quote:
Originally Posted by Hagar
Thanks everyone for the comments. I am leaning towards the second one myself which is the way I will probably go with my Flat files. There has been a lot of talk about the saturation of flat files for the QHY8 on this and other forums without any real resolution to what is best.
Be my Guest to tinker with the images. The only way we learn is by listening and watching others attempts at the same task. A different perspective to an image is never a waste.
Thanks Again.
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Doug.
I like the second one.
As for the flats, the flat needs to be in the linear part of your sensor otherwise when you divide by them they will give an incorrect result. This was discussed on one of the photometry groups as the linearity is important for photometry.
Your sensor on the QHY8 is an antiblooming sensor and is probably not particularly linear above about 1/2 the saturation level.
You could try and measure the linearity by taking a series of images of the same star field with a bright star that will saturate the sensor and some dimmer ones that don't. Expose for increasing times in ~10 sec increments. ie 10,20,30,40,50 sec etc until you have saturated the bright star. You need to start with an exposure that doesn't saturate the stars.
You then measure the flux of a few stars in the images and graph the results against time.
This assumes that the stars you are imaging are not variable in the short term and that no clouds etc have stuffed up some of the images.
The results you get will look like the attached charts.
After doing this you can pick what intensity is linear for your CCD and keep the flats within that range.
Cheers
