Dear colleagues, We have made a rough measurement of the throughput of the 3.5m, using the Seaver Prototype Imaging camera (SPIcam). A object with R=20 produces about 120 e/sec in the thinned SITe detector. Using the vendor's characterization of the chip's QE, and the site's posted filter transmission curve, and assuming each of the three mirrors reflects 80% of the light, we only see about 56% of the light I compute we should see in the focal plane. One of the assumptions above must be incorrect, or I have made an error (or both!). I think it most likely that the mirror performance is the culprit. Note that we are planning to realuminize the mirrors in december. A more detailed writeup is available off my homepage, http://www.phys.washington.edu/~stubbs/ APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 99 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