The ESI CCD is a high-resistivity MIT-Lincoln Labs 2048 x 4096 device with 15 µm pixels. The controller is a Leach 2. The CCD can be operated in either single-amplifier or dual-amplifier mode, selectable under software control. There are also 3 software-selectable readout speeds (fast, normal, and slow), and two software-selectable gains (low and high).

The default mode of operation is dual-amplifier readout, fast readout mode, and low gain. At this point, the ``normal'' readout speed provides no advantage, either in readout noise or CTE. The default mode is ``fast''. However, we have retained the three speeds in case this proves useful if we switch to another CCD in the future.

The high gain is also of marginal use with this CCD. In low gain mode the readout noise is 2.1 DN, enough to avoid significant quantization noise. The ADC limit of 65,535 DN corresponds to 80% of the full-well depth in low gain. In high gain the ADC limit is only 30% of full-well depth.

Table 4

ESI CCD Characteristics
Full-well depth
Read noise
Dark current (-120C)
2 e-/pix/hour
Gain (low)
1.29 e-/DN
Gain (high)
0.5 e-/DN
Serial CTE (fast readout)
Serial CTE (normal readout)
Serial CTE (slow readout)
Readout time (fast)
39 sec
Readout time (normal)
57 sec
Readout time (slow)
120 sec


There are eight bad columns and a bright area, all in the lower left part of the CCD. There are also a few marginally bad CTE spots on the detector, although these are not always obvious on images.

9.1. Binning

You can bin the pixels in 1x2, 2x1, or 2x2 patterns. However, note that the serial registers on this CCD are roughly the same size as an individual pixel, meaning that when you bin you must still keep the binned pixel below 105,000 electrons. (Many other CCDs have serial and output registers which are two to four times deeper than a pixel, so that binning 2x2, say, allows you to fill each individual (unbinned) pixel to maximum depth.) In practice, even with unbinned pixels the ADC limit is reached before the pixel full-well depth, and so the maximum number of DN per pixel, binned or unbinned, is always the ADC limit of 65,000.

9.2. Quantum efficiency

The current CCD has very good quantum efficiency (QE) from 3900 Å to over 8000 Å, dropping significantly by 10,000 Å and beyond.

Table 5

3200 Å
3500 Å
4000 Å
4500 Å
5000 Å
6000 Å
6500 Å
7000 Å
8000 Å
9000 Å
10000 Å