NOTE: The Loral chip which serviced us well for several years died in early April 2001. A replacement Loral (SN1259, Lot 3A, W2-(0,0)) was put into service on April 17, 2001. This chip has a 3 bad column on one end, and slightly poorer QE in the U, but similar full well and noise characteristics.
Perkins 72inch Hall 42inch
Number of pixels 2048x2048 2048x2048 2048x2048 800x800 2048x2048
Pixel size ? µm 15µm 24µm 15µm 24µm
Field of View 13.3' x 13.3' 3.2' x 3.2' 5.2' x 5.2' 5.7' x 5.7' 19.4' x 19.4'
Gain* 3.3 e/ADU (default) 3.2 e/ADU (default) 3.9 e/ADU (default) ? e/ADU 3.9 e/ADU (default)
Min. exp time for <1% timing 3 sec ? 5 secs ? 5 secs
Readnoise* RMS 13 e 15 e 11 e ? e 11 e
Focus BVRI +3800Abs (at 40F) -30Abs (at 62F); +360Abs (at 45F); +800Abs (at 35F) +2400Abs (at 32F) +3240Abs (at 41F) +3480Abs (at 20F) 2.4 volts
Focus step size +50 +50 +50 +50 +0.01 volts
Quantum Efficiency ? Loral QE plot* SITe QE plot* No response <4000A SITe QE plot
Count Rates at U=B=V=R=I=20th mag at X=1.0
U ? e/sec/image 12 e/sec/image 8.5 e/sec/image ? 2.0 e/sec/image
B 42 e/sec/image 65 e/sec/image 48 e/sec/image ? 8.7 e/sec/image
V 61 e/sec/image 88 e/sec/image 65 e/sec/image ? 14 e/sec/image
R 67 e/sec/image 88 e/sec/image 78 e/sec/image ? 17 e/sec/image
I 45 e/sec/image 54 e/sec/image 52 e/sec/image ? 9.2 e/sec/image
Setup position relative to "home" RM: 0" north; 0" east RM: 10" north; 30" east RM: 10" north; 30" east RM: 10" north; 30" east RM: 260" north; 24" west
Orientation N: up; E: left N: up; E: right N: down; E: left N: ?; E: ? N: down; E: left
Binning 1x1 2x2 1x1 2x2 3x3 4x4 1x1 2x2 4x4 1x1 2x2 1x1 2x2 4x4
Scale 0.390"/pix 0.096"/pix 0.191"/pix 0.287"/pix 0.382"/pix 0.153"/pix 0.306"/pix 0.612"/pix 0.43"/pix 0.86"/pix 0.568"/pix 1.136"/pix 2.272"/pixl
1% linearity limit <148,000e (<45,000ADU) <? e (<? ADU) <80,500e (<26,000ADU) <80,500e (<26,000ADU) ? ? 183,000e (47,000ADU) A/D limit: (64,000 ADU) A/D limit: (64,000 ADU) 40,000e? 80,000e? 183,000e (47,000ADU) A/D limit: (64,000 ADU) A/D limit: (64,000 ADU)
Readout time* 45 secs 4 secs 23 secs 6 secs 3 secs 1.5 secs 235 secs 55 secs 18 secs 20 8 235 secs 55 secs 18 secs

*Notes: The Loral CCD has an adjustable time-constant which affects the gain, read-out time, and readnoise. By default this is set to 2 µs, with the resulting readout times, gains, and readnoise listed above. For 1µs decrease the readout times by a factor of 1.5; for 6µs, increase the readout times by a factor of 2.6. At 1µs the gain is 6.3 e/ADU and the readnoise 20e; at 6µs, the gain is 0.2 e/ADU and the readnoise 15e. Unbinned (1x1) with a time constant of 6µs does not work.

Similarly a time-constant can be adjusted on the SITe CCD by explictly adjusting the gain; however, the large overhead per pixel results in little improvement in the readout time.

The QE plots for the Loral and the SITe were measured by different means. The Loral numbers are fairly solid, while the SITe numbers are believed to be artificially low in an absolute sense.

For further information about the SITe CCD see the status memo by Ted Dunham.

Last updated 28 Dec 2001