The instrumental functions of the two-étalon system with a finite field of view have been examined in cases in which both étalons are inclined against the optical axis. The average transmittances of the rays in the finite field of view are obtained by numerical integration. It is shown that the line shape of the instrumental function becomes asymmetric, varying not only with the zenith angles of the symmetry axes of the two étalons but also with their azimuth angles. Experimental measurements of line shapes with the He–Ne laser show the asymmetric feature predicted by the calculation. The simulation calculations for the two-pass étalon system are also carried out and show a drastic discrepancy in transmittances between azimuth angle differences of 0° and 180°.
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