On the transmission of light through tilted interference filters
  The transmission characteristics of commercial interference filters are not quite what we expected from the specifications provided by manufacturers. The unexpectedly sharp dependences of the transmission coefficient on the incidence angle, wavelength, and on the position where the light beam falls on the filter may be important in the analysis of systematic effects in experiments incorporating interference filters. 
A. O. Sushkov, E. Williams, D. Budker