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Efficiency

A major advantage of CCDs is their high efficiency. The nominal wavelength response for the two types of CCD currently in use on La Palma is shown in Figure 2.1. The RCA SID501 has a peak efficiency of about 75 per cent, whilst the GEC P8603 has a peak efficiency of about 55 per cent. Both chips have a useful sensitivity over most of the optical/near IR spectrum. Note however that although the useful response of the GEC P8603 extends down to the atmospheric cutoff at about 3000 Å, the response of the RCA SID501 cuts off sharply below about 3500 Å. Our measurements however indicate that the blue performance of the RCA is significantly worse than this, and is completely useless in the U band. The GEC response is close to that shown.