The classical method of discovering objects that vary in position and/or time is to examine well-matched pairs of plates using a blink comparator. This method, being manual, is slow, subjective and, unless several matched plate pairs are used, suffers from incompleteness. The combination of wide angle Schmidt cameras, high speed measuring machines and sophisticated computer software has enabled objective methods for searching for variable objects to be devised. Using such methods it is possible to intercompare stacks of plates digitally. The deepest plate may be used as a master in position and magnitude, eliminating the need for the rest to be well matched. Following measurement and analysis it is a relatively simple matter to prepare lists of variable objects such as RR Lyrae stars, Mira long period variables, cataclysmic variables, active galaxies, comets and asteroids which may then be used as a basis for more intensive study by smaller dedicated instruments.This, however, is only one aspect of the cooperation possible between Schmidt telescopes, measuring machines and small telescopes. In projects involving the study of large numbers of mainly non-variable objects (stars or galaxies) the small telescope has a most important role to play in providing photoelectric magnitude calibrations to convert machine measured magnitudes to a standard system. To date this has been the principal use to which the small telescope has been put, even in the study of the distribution of faint galaxies from Schmidt plates it was a small telescope which provided the necessary measurement of the background sky brightness.A further dimension is provided by the addition of an objective prism to the Schmidt camera. In this case objects readily detected include emission line stars and galaxies. The calibrating power of the smaller instrument is now of value in providing standard galaxy radial velocities to calibrate red shifts measured from the very low dispersion prism.
Objective-Prism Redshifts of Faint Galaxies
