In our runs since the realuminization, Tom Harrison and I have noticed variations in focus across the GRIM II field of view. To see what I mean, look at ftp://oldp.nmsu.edu/pub/alan/apo/970208/bad.fits ftp://oldp.nmsu.edu/pub/alan/apo/970208/good.fits These are stacks of 8x60 second object/sky exposures. A good stretch is -20 to 100. Ignore the flat-topped saturated stars. In the good frame, the FWHM is constant at about 2 pixels across the field. In the bad frame, the FWHM varies from about 2.5 pixels in the upper right to 5 pixels in the lower left, where stellar images ARE DOUGHNUTS. One pixel is about 0.5 arcsec in these images. The image quality, when it varies, always seems to be in the sense of the lower left is poorer than the upper right. However, we've only really been looking at objects in a fairly restricted part of the sky. Our hypothesis was that the telescope and the re-imaging optics in the instrument were being brought out of collimation as the telescope moved and the instrument rotated. To that end, Mike Ledlow and I took images of M5 at 0, 60, 120, 180, 240, 300 degrees of rotation during the engineering run last week. This effect is present in many of the images, but the seeing is sufficiently bad that it is is not very obvious and it's difficult to tell what is going on. At this point there is not much more I can do, but this problem remains very serious. Alan Watson APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 34 in the apo35-grim archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-grim/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-grim@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO