CCD CharacteristicsNOTE: 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 | ||||||||||||||
| NEW PRISM | NEW Loral (SN1259) | SITe | USNO 4:1 | SITe | |||||||||||
| 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: right | 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 | <148K e (<45K ADU) | <? e (<? ADU) | <80K e (<26K ADU) | <80K e (<26K ADU) | ? | ? | 183,000e (47K ADU) | A/D limit: (64K ADU) | A/D limit: (64K ADU) | 40K e? | 80K e? | 183K e (47K ADU) | A/D limit: (64K ADU) | A/D limit: (64K 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 |
1. 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.
2. 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.
3. 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.