Note that dewar #13 is no longer available and that dewar #8 now contains a 2048x2048 LBL high-resistivity CCD. Its QE is very roughly comparable to dewar #6. Other characteristics differ. For more on these CCD's see section of this manual on individual components or contact a member of the Mount Hamilton support staff. T.M. December, '03

The Hamilton throughput plotted below was measured, using a standard star, in 1990, for both the 3-meter and the CAT. At that time the only available CCD was a thinned, 800x800, TI device in dewar #8 (now replaced -- see above). The throughput curves shown here use those 1990 data, but scaled to the QE's of two 2048x2048 CCD's which were used for much of the last 10 years: the unthinned chip in dewar 13 and the thinned chip in dewar 6. Since then, #13 has gone out of use; #6 is still in regular use; #8 has been resurrected wih an unthinned, 2048x2048, high-resistivity device with QE (and therefor total throughput) comparable to, or better than, #6. See also Detector Characteristics.

Bear in mind that Hamilton performance, particualarly with the 3-meter, is strongly seeing-dependent. The throughput measurements were made with a 4-arcsecond slit in 1 to 2 arcsecond seeing; the typical 3-meter observing slit is just over 1-arcsecond.

Throughput with 3-meter

Throughput with CAT

Note the change in the Y-axis scale of the CAT plot compared to the 3-meter plot. The better relative performance of the CAT results from the larger projected slit afforded by that telescope's more favorable plate scale. (On a typical night, the CAT's performance is only about a factor of seventeen less than the 3-meter's, rather than the factor of twenty-five predicted by relative apertures alone.)