with this detector has been very promising, and the first attempts lead to the restoration of a triple star (Aristidi [*et al.*]{}, 1997).

– The principle of the PAPA camera was described in Papaliolios and Mertz (1982) and Papaliolios [*et al.*]{}, (1985). It features a two-stage electrostatic amplifier, and a fast (P46) phosphor. Amplified photon impacts are analyzed by a set of binary masks which act as an optical computer to instantly digitize the position of photons in the field. The version we used was new and not fully operational, with a new binary mask setup and a refurbished image intensifier jointly made by P. Nisenson, D. Gezari (CfA) and L. Koechlin (OMP). The first observations in June 1997 have shown that the quantum efficiency was very good, slightly larger than that of the CP40. The maximum photon rate per second was as high as 100,000 but a small “hole” at the center of the autocorrelation function was also noticed. The geometric distortion caused by the image intensifier was large and an overall scale variation during the night imposed quasi permanent scale calibrations. To solve this problem, the image intensifier was changed after these observations.

[*4.4. Comparison of the detectors*]{}

