Next: The CCD detectors
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The IPCS detector is based on the principle of event centering: Incoming photons on the light-sensitive target are amplified by an image-tube intensifier; the light flashes at the output window are registered by a Vidicon or CCD detector. That signal is analyzed by hard-wired logic to determine the positions of individual photon events. The sensitivity of the IPCS is determined by the characteristics of the Image Tube phosphorus. The IPCS is sensitive up to about 7000Å, with an overall Quantum Efficiency of about 20%. In practice the IPCS is only used for observations where the signal-to-noise is limited by the detector, i.e. high dispersion spectroscopy on faint objects (in dark time).
A first-generation IPCS has been in use at the IDS spectrograph (INT) until about 1992. This detector made use of a Vidicon tube for event detection, and therefore required elaborate set-up procedures for alignment and minimizing of image distortion. Image size is maximum 2048256 pixels, but for spectroscopic use a format of 204832 is more typical. Pixel size is usually 15 in the dispersion direction. Calibration of this detector can be cumbersome and, in particular for longslit spectroscopy, special calibration exposures are needed. These calibration are marked in the catalogue with special codes.
A second-generation IPCS with CCD readout has been in use at the WHT instruments (ISIS and UES) since 1991. Maximum format is about 24003200; pixel size 12.