************************** sorry, the g' efficiency in item 2 should be 0.100 instead of 0.100, typo. correct message attached below *************************** Dear DSC users, I repeated the efficiency calculation similar to what posted ealier by Kris Stanek on 3.5m + DSC + SDSS filter + CCD system, the result is similar to what Kris got. Details are : 1. Based on observations of Oke-Gunn standards under SDSS filters during Feb08/09, 09/10 nights. Both nights are ~0.01mag level photometric nights. 2. Total efficiency of the system ( no correction for filter transmission, reflection, secondary, in the sense identical to the previous measurement of Stanek): u' : 0.027 ** g' : 0.100 r' : 0.173 i' : 0.144 z' : 0.085 Stanek's value which states 0.14 for v filter is quite consistent with current measurement. The above numbers assume the central wavelength and FWHM of SDSS filters as given in Fikugita et al. Richmond took the new filter transmission curve posted recently by Jim Gunn and convlove it with Oke-Gunn standards. The results are L u' : 0.036 g' : 0.110 r' : 0.167 i' : 0.136 z' : 0.038 3. When assuming 0.85 reflection (three times) and secondary : u' : 0.045 g' : 0.166 r' : 0.290 i' : 0.242 z' : 0.143 4. In Fikugita et al. paper on SDSS filter system, they assume the filter transmission and CCD Q.E. curve, and give the predicted number of photons per cm^2 in SDSS filters, below are the ratio of what I measured to what they predicted under a 3.5m telescope and three times 0.85 reflectivity : u' : 0.332 g' : 0.444 r' : 0.695 i' : 0.718 z' : 0.641 which means this system is sth like 1/3 to 2/3 efficient as it should be. -- Xiaohui Fan Princeton University Observatory Peyton Hall Princeton, NJ 08544 email : fan@astro.princeton.edu tel : (609) 258-5153 (O) (609) 683-1315 (H) APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 25 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