The choices you've suggested make a lot of sense to me. The one other choice I could see some people interested in would be, medium red, medium blue. This covers the full spectral range, and gives somewhat better dispersion in the blue. If read noise is not an issue (and I haven't gone through the numbers to find out if this is the case) then this might be superior to the medium red, low blue combination you suggest. What counts here is not just the number of angstroms per pixel (properly called the dispersion), but the number of angstroms per *resolution element*. The latter depends on the width of the slit, but is it possible to get estimates of the angstroms per resolution element for a 1.5" slit, for the different gratings? Thanks, Michael Strauss APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 556 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