Heidi Newberg and I have used the DSC on the 3.5-m several nights recently, and we have come to several conclusions: 1. If the baffle is not in place when the DSC is used, scattered light (from beyond the tertiary, probably) enters the camera. So, use the baffle (and move it as close to the primary as possible). 2. There appears to be a light leak in the filter slide, even if it is covered with tape. We asked Eddie to shine a flashlight at the filter while taking a dark exposure, and got a lot of light in a roughly circular blobby pattern at the center of the image. 3. There appears to be a _different_ light leak in the shutter. We asked Eddie to shine a flashlight in the aperture of the camera when it was dismounted from the telescope, and got quite a different pattern of light on the chip. 4. The new overscan rows help to remove the bias signature from each individual image. Rah. Preliminary analysis of some repeated imaging of the same fields seems to show that 40 minutes of exposure in Harris R-band with 1.7 arcsec seeing yields a S/N around 10 for R=23. Oh, and, most important, clouds cover the mountain when Heidi's time begins, and leave JUST when her time is up. This is the 3rd time in a row that it has happened .... Michael APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 31 in the apo35-dsc archive. You can find APO the archive on http://astro.princeton.edu:82/apo35-dsc/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-dsc@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO