[Aavso-photometry] Need Advice, CCD photometry;

[Michael Newberry]

> Dan wrote:
>>    ---
>>   Mike K. and Justin P.:
>>    After you guys mentioned sigma clip processing, I went on a search to 
>> find 'better' algorithims and I'm quite satisfied with what I've found. 
>> Infact, I have chosen an alogorithm entitled SD mask, which incorporates 
>> the best of sigma clip, median, and average.  If you guys have any 
>> suggestions on the prefferred settings for these algorithms, I'd love to 
>> here them.  I've also discovered that when combining there's another cool 
>> algorithm to use entitled bicubic resampling, do you guys have any 
>> experience with this?  Do you also use SD mask or sigma clip when 
>> combining your images or just for calibration frames?
>>

 Dan, be really careful on jumping in like this.  I strongly suggest
to all beginners that you just use average, or at most median, for
photometric image stacking until you really understand the process.
Almost all sophisticated methods use specialized knowledge of your
system (gain/readnoise) or of the sky conditions in order to obtain
their improvement, and if you don't understand what is going on, you
are likely to end up with a pretty image, but one that is useless for
precision photometry.  My usual test is to compare any rejection scheme
against a pure average.  You had better obtain the same results on
well-exposed stars, and consistent results on fainter ones.

Photometry is much like making soup.  You start with basic ingredients
and then start experimenting with different spices and combinations.
You don't add everything at the beginning and hope to get something
you will like.

Arne