Fabry–Prot etalons illuminated with collimated beams have been analytically characterized in detail since their invention. Meanwhile, most of the features of etalons located in telecentric planes have been studied only numerically, despite the wide use of this configuration in astrophysical instrumentation for decades. In this work we present analytical expressions for the transmitted electric field and its derivatives that are valid for etalons placed in slow telecentric beams, like the ones commonly employed in solar instruments. We use the derivatives to infer the sensitivity of the electric field to variations in the optical thickness for different reflectivities and apertures of the incident beam, and we compare them to the collimated case. This allows us to estimate the wavefront degradation produced by roughness errors on the surfaces of the Fabry–Prot etalons and to establish the maximum allowed rms value of the cavity irregularities across the footprint of the incident beam on the etalons that ensures diffraction-limited performance. We also evaluate the wavefront degradation intrinsic to these mounts, which is produced only by the finite aperture of the beam and that must be added to the one produced by defects. Finally, we discuss the differences in performance of telecentric and collimated etalon-based instruments and we generalize our formulation to anisotropic etalons.

用准直光束照射的 Fabry-Prot 标准具自发明以来就已得到详细的分析表征。同时，尽管数十年来在天体物理仪器中广泛使用这种配置，但位于远心平面的标准具的大多数特征仅在数值上进行了研究。在这项工作中，我们提出了传输电场及其导数的解析表达式，这些表达式适用于放置在慢速远心光束中的标准具，就像太阳能仪器中常用的那些。我们使用导数来推断电场对入射光束不同反射率和孔径的光学厚度变化的敏感性，并将它们与准直情况进行比较。这使我们能够估计由 Fabry-Prot 标准具表面上的粗糙度误差产生的波前退化，并确定标准具上入射光束足迹的空腔不规则性的最大允许 rms 值，以确保衍射限制性能。我们还评估了这些安装座固有的波前退化，这仅由光束的有限孔径产生，并且必须添加到由缺陷产生的孔径上。最后，我们讨论了基于远心和准直标准具的仪器的性能差异，并将我们的公式推广到各向异性标准具。我们还评估了这些安装座固有的波前退化，这仅由光束的有限孔径产生，并且必须添加到由缺陷产生的孔径上。最后，我们讨论了基于远心和准直标准具的仪器的性能差异，并将我们的公式推广到各向异性标准具。我们还评估了这些安装座固有的波前退化，这仅由光束的有限孔径产生，并且必须添加到由缺陷产生的孔径上。最后，我们讨论了基于远心和准直标准具的仪器的性能差异，并将我们的公式推广到各向异性标准具。