Aperture plates

For multi-object spectroscopy, the acquisition of the field is performed by means of an aperture plate of type FOCAP. This aperture plate is a 3mm thick brass plate. The plate is drilled at precise locations with holes to accept fibre connectors. The holes must be made for each of the three types of connectors: for the individual fibres, for the two semi-coherent bundles and for the coherent bundle. The characteristics of the holes are specified in the Table (it is assumed that the OY+ direction corresponds to the North direction during the observing epoch).

A high precision (on the order of 20m) both for the coordinates and the hole diameters is fundamental for accurate field acquisition.

The number of holes to be performed for each type of connector is as follows:

• for individual fibres: -- one hole for each target -- one for each sky area to be sampled
• for the semi-coherent bundle: -- one hole 400" North of the field centre (relative to observing epoch) -- one 400" South of the field centre (relative to observing epoch) -- one for each guide star for manual guiding (two at least)
• for the coherent bundle: -- one hole for the field centre -- one for the guide stars chosen for telescope tracking (one at least).

Potential users should make their own arrangements for the manufacture of aperture plates, through one of the principal contacts for this instrument.