The recently developed Kodak emulsions IIIa-J and IIIa-F have been used as a new tool for deep-survey photometry. Among their most useful features are the following: (i) fine to very fine granularity; (ii) very high resolving power; (iii) high sensitivity over a large wavelength range in the optical part of the spectrum.

Some numerical results obtained from scanner data of a variety of normal star types, and from the spectral sensitivities of these Kodak plates combined with various optical filters are presented. We study the effects of these filters on the resulting synthetic colors with respect to the intrinsic potential of the colors to classify faint stars. In addition we briefly discuss the effects of interstellar reddening and the calibration of the photographic colors through photoelectric UBV photometry.

This synthetic approach to multicolor photometry is discussed in the more general context of the relations between spectral classification, stellar photometry, and model atmosphere calculations. This context is the natural basis for galactic astronomy.