Hello everyone, Last night I tried to do some simple flat-fielding for the DIS slit-viewer and wanted to see how faint we can acquire. After substracting a rough bias level, and flat-field it with a supersky from a previous night, a 3 min slit viewer exposure goes quite a bit deeper than the SDSS finding chart I have. So the limiting magnitude should be something like 23.5 mag, and this is under 1.5" seeing. We have been doing spectroscopy of very faint sources recently, and I found the flat-fielding makes object acquisition a lot easier. Cheers, Xiaohui -- Xiaohui Fan School of Natural Sciences Institute for Advanced Study Princeton, NJ 08540 email : fan@sns.ias.edu tel : (609) 734-8023 (O) (609) 279-2981 (H) APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 83 in the apo35-dis archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-dis/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-dis@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO