  The determination of the galaxy luminosity function is an active and
fundamental field in observational cosmology. In this paper we propose a cost
effective way of measuring galaxy luminosity functions at faint magnitudes. Our
technique employs the use of galaxy redshifts estimated from their multicolor
photometry (Connolly et al. 1995). Associated with the redshift estimate is a
well defined error distribution. We have derived a variant of Lynden-Bell's
(1971) C--method that considers, for each galaxy, the probability distribution
in absolute magnitude resultant from the redshift error. This technique is
tested through simulations and potential biases are quantified. We then apply
the technique to a sample of galaxies with multicolor photometric data at
moderately faint (B=23) limits, and compare the results to a subset of these
data with spectroscopic redshifts. We find that the luminosity function derived
from the photometric redshifts is consistent with that determined from
spectroscopic redshifts.
