To try and pin down the cause of the discrepancy between Michael's S/N calculations and his limiting magnitude, I matched stars from the Koo-Kron photographic catalog to objects detected in one of the SA57 scans. I found that 1. S/N ~10 at F= 20, in agreement with Michael's revised estimate 2. S/N began dropping below 3 at F ~21 3. At 21 < F <= 22, photo found 41% of the objects (with consistent flux measurements) 4. At 20 < F <= 21, photo found 95% of the objects. 5. Fainter than F=22, there were no reliable matches. 6. Overall, for F <= 22, the completeness was 80% These numbers are consistent with Michael's estimate of S/N and expected detection rate for *point* sources. I believe the catalog he used contained both galaxies and stars without any classifications. The inclusion of galaxies probably explains the lower completeness. If people are interested, I can make my plots available on the web. Nan APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 4 in the apo35-dsc archive. You can find APO the archive in /u/strauss/apo/mailer/apo35-dsc on astro.princeton.edu APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-dsc@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO