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Hi allI have been working trhough my research material, and the photometry pipline I'm building to date, and a couple of questions have arizen?1. When combining frames using combine what would be the "best" reject parameter to use: minmax, ccdclip, crreject, sigclip, avsigclip, pclip?2. How can I scale darkcombine according to temperature? Our darkframes are temperature "variant".3. Is there a tool available in IRAF to pick apperture size. How would I go about determining the difference between two appertures, and plotting the difference?4. Why and how are histograms plotted when determining the FWHM of a star in IRAF?5. Why and how do photon statistics play a role in the variation of images, and in the core of subtracted psf images? Hope U understand the Q!6. In general, what can cause variation on ccd chips? Like positional pattern.7. Finally. Are the same photometric methods applicable on crowded-fields as on non-crowded-fields, i.e. can I use psf-fitting on both?Thanx for the helpRegards
Pat

Hi allI hope I'm not becoming a burden , or are the Q's harder than I thought!Some reaction would be nice, please. If you don't have time, I understand. My time is limited as well. :wink: Thanx for all the previous help. It is a blessing for the IRAF comunity to have such great support. I deffinatly appreciate it. Thanx
Pat

VERY good Qs!!!
Hope, one day answer will be here... :