A general expression is derived for a Fabry-Perot spectrometer when one or more of the functions entering into its description lack the inherent radial symmetry of the fringe pattern about the etalon optical axis. Calculations of the effects of these asymmetric functions applicable to densitometry of photographic fringe records and vidicon scanning of fringe patterns are given. The theory is also applied to interference filters in order to quantitatively explain their behavior as they are tilted in order to scan a spectrum. Rather simple approximations to the theory are also derived for interference filters that show that both the inverse of the peak transmission and the square of the width (normalized to the unbroadened filter) are proportional to the square of the product of the tilt and field of view angles over the width, in excellent agreement with experimental measurements.
G. Hernandez, "Analytical Description of a Fabry-Perot Spectrometer. 3: Off-Axis Behavior and Interference Filters," Appl. Opt. 13, 2654-2661 (1974)