High-fidelity copying of large-area astronomical plates - Principles and some practical results

We report here on an investigation into the achieved fidelity of copies of a large Schmidt telescope plate. Atlas quality copies both on glass and film and the original are compared. Two glass copies made through different intermediate positives are used to look at the fidelity of the separate positives. We confirm the general belief that glass copies are capable of impeccable photogrammetric quality. However, film copies are shown to achieve essentially the same astrometric fidelity. The general feeling that for photometric applications film copies should be equivalent to glass ones is not confirmed. We find that glass copies are generally better in densitometry