described in Clamping and Paresce (1989)) has been built by the Space Telescope Science Institute (Baltimore). The model we used was lent by the Observatoire de la Côte d’Azur (OCA) for some observing runs between 1993 and 1996.

This detector has a S20 photo-cathode and a saturated mode single microchannel amplifier (Gen II). The position analysis of the detected photo-events is made with a resistive anode. Each cloud of amplified electrons, resulting from the impact of a photon on the photo-cathode, produces a charge drift towards the four electrodes which surround the resistive anode. The location of the impact is deduced from the voltage variations et the electrodes and can be measured accurately to about 10 kHz.

Compared to the CP40, the quantum efficiency of the Ranicon is smaller by a factor of $\sim$3. This is due to the lower efficiency of the GEN II compared to the GEN I intensifiers.

Although the micro-channel amplification does not introduce geometric distortion, we have noticed a small distortion with the X and Y axes which are not perfectly perpendicular. A small variation of the geometric scale was also noticed and calibration was needed during the night.

Another unexpected defect was the presence 