The continuing confusion about where the UV hit in DIS is taking place is confusing to me. The problem is with the dielectric reflective coatings in the schmidt camera and on the prism. I built a system with a uv diode, filters, and a mercury lamp which compared 3650/63 with 4046 and 4358. In the camera block the antireflection coatings were measured by shining a beam through the block and out the hole, meeting no reflective surfaces. The antireflection coatings so tested, those on the collimator, and those on the schmidt corrector plate, were all as specified. (These tests also dispel any doubts about the cements in the camera). The reflective coatings, however, were not, and showed very small reflectance at 3650; the losses in the camera (2 reflections) were approximately the square of the losses in the prism (1 45 degree reflection). I no longer have those records, they being at least two disk crashes removed, but they were reported, I believe, on this forum. It WAS a long time ago. --jim APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 502 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/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-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO