MOSAIC reduction is very difficult. http://www.noao.edu/noao/noaodeep/ReductionOpt/frames.html has the official instructions. Important things: Have the latest version of MSCRED and MSCDB installed. Both will give cryptic errors or "cannot open file" errors (because the files don't exist) otherwise. mscredsetinstrument kpno CCDMosaThin1msccmatch obj09*.fits coords="!mscgetcat $I $C" search=60 rsearch=1 nfit=30 accept=yes interactive=no fit=no