Spectra recorded by Michelson interferometer spectrometers are usually distorted because the spectrometers have a finite resolving power. Indeed, although the radiance spectrum is obtained in principle by a Fourier transform of the interferogram, various factors intervene to make the recovered spectrum an imperfect representation of the true spectrum. The most important ones are: a)- aperture effects; b)- tilt and aberrations; c)- phase and compensation; d)- truncation; e)- noise.