of a small “hole” at the center of the autocorrelation function, similar in some way to that of the CP40 (cf, §4.2), but with a smaller amplitude. This is caused by the depletion of electrons of a micro-channel after a photon-detection: a delay of a few tenths of milliseconds is needed to recover its full charge and efficiency. To reduce this defect, the photon flux had to be lowered to about 8000 photons/sec.

[*4.3. Other detectors*]{}

10000 Two other detectors have been used with PISCO: the ICCD (Intensified Charge Coupled Device) belonging to C. Aime and E. Aristidi’s from Nice University, and P. Nisenson’s PAPA camera from Harvard Smithsonian Center for Astrophysics (CfA):

– The ICCD has a single stage intensifier. It cannot operate in true photon counting mode and is thus limited to objects brighter than V$_{lim} \sim$10. This detector has no significant geometric distortion nor non-linearity problems which would affect the photometry measurements. The exposure time can be set between 64 $\mu$sec and 16 msec and the gain of the micro-channel amplifier can be tuned, thus allowing a wide range of input luminosities. The output is an analog video signal, recorded on SVHS video cassettes. Bispectral image restoration 