Micheal has made an update to his primer. I have not incorporated his changes into my version.
Brian Yanny also wrote an introduction to the SDSS FITS binary tables with a quick tutorial on how to find objects with strange colors. He includes an handy-dandy TCL script, which makes a good starting point.
At fermilab is a quick description of the calibrated objects file. This is a calibrated version of the OBJC photo output file.
It is very important to understand the flags that photo sets, and what they mean.trq, June 16, 1999