I'm having a rough time trying to get rid of stars in my master flats. I haven't had this issue before but now I'm using a friends remote system and no matter how I do it I get stars in the master flats. 10-12 flats near zenith, mount tracking stopped -- all the usual stuff.

What is the best method in CCDS to get rid of the stars?

Tom

Hi Tom,

First try varying the parameters available in the "Master Flat" process. In particular, I recommend "clip min/max" with "auto" normalization and an aggressive number for max rejection (e.g. for 10 flats, try entering max = 6 and min = 2). But the best approach is to create the master flat via normal stacking procedures:
1) Calibrate (dark subtract)
2) Normalize – Control; scalar
3) Data Reject – try various methods (including aggressive min/max) and blink the stack to verify that all the stars are rejected.
4) Combine; mean
5) Save

It may be that 10-12 late-twilight frames are not enough. If they are taken too late then it may not be possible to remove every bit of every star. But don’t worry too much about dim residual stars in the flat as it is unlikely that they will be visible in the processed images (which is fine for pretty pix but if you are doing photometry then you need to improve your flat taking conditions).

Stan

Tom,

You don't say whether you are dithering your flats or not. A modest mount movement between flat exposures will aid in removing the stars when combined using some of the techniques Stan mentioned.

CCDAutoPilot automatically dithers flats by an appropriate amount. I take flats with maximum exposures of 70 sec. Individual flats almost always show stars and a Poisson Sigma Reject after normalization removes stars completely.