 The technique relies upon the spectrum of radiation being emitted by the object having strong features that can be detected by the relatively crude filters.As photometric filters are sensitive to a range of wavelengths, and the technique relies on making many assumptions about the nature of the spectrum at the light-source, errors for these sorts of measurements can range up to δ"z" = 0.5, and are much less reliable than spectroscopic determinations.In the absence of sufficient telescope time to determine a spectroscopic redshift for each object, the technique of photometric redshifts provides a method to determine an at least qualitative characterization of a redshift.