Looking at two frames near NGC 2419 that I took last night with the DSC + SDSS i'-band filter, I can find 8 stars which appear in the Hubble Guide Star Catalog. The stars are spread over an area about 7.5 x 2.5 arcmin. Solving for the plate scale with these 8 stars, I get plate scale = 0.281 +/- 0.001 arcsec/pixel I also note that the "quick look" routines in 'shiver', the ones which act when on runs 'rview', clicks on Cursor and then points to a star and presses Right Button, don't seem to give the correct value for FWHM. Last night, I consistently got values of "3.2" or "3.3" when I used the 'rview' routine; taking that printed value as the FWHM in pixels, I thought the seeing was about 0.9 arcsec! But in the morning, I looked at one frame and carefully measured FWHM ~ 6.9 pixels = 1.8 arcsec. Maybe I misunderstand the number that is printed by 'rview'. Perhaps that's the Half-Width at Half-Max, in pixels. If so, then it _does_ yield a pretty good answer. In that case, my apologies for casting aspersions on it :-) Michael Richmond APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 10 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