A spatial Fourier transform spectrometer is disclosed (e.g., 350). The Fourier transform spectrometer includes a Fabry-Perot interferometer (e.g., 320, 420, 520) with first and second optical surfaces (e.g., 454, 458, and 554, 558). The gap (e.g., 462, 562) between the first and second optical surfaces spatially varies in a direction that is orthogonal to the optical axis (e.g., 466, 566, 666) of the Fourier transform spectrometer. The Fabry-Perot interferometer creates an interference pattern from input light. An image of the interference pattern is captured by a detector (e.g., 340, 640), which is communicatively coupled to a processor (e.g., 342). The processor is configured to process the interference pattern image to determine information about the spectral content of the input light.