A calculation method for evaluating UV optical filters, suitable for fluorescence detectors (FD), such as the one from the Auger Project and other similar cosmic ray observatory setups, is presented. We have considered the adopted geometry of a telescope based on a spherical mirror and a camera consisting of a photomultiplier pixel array. In the calculations, an angular weighting factor is introduced, which affects the results of the optical filter performance. Two optical filters, of the interference and absorption type, are evaluated using this method. Experimental measurements of the spectral transmittance of the filters for various angles of incidence are made by a double beam spectrophotometer. To calculate an overall performance, the most dominant spectral lines of the atmospheric fluorescence are used, modified by the atmospheric transmission coefficients. This performance is determined by the detection efficiency of the pixel detector (photomultiplier) with the optical filters used.