The paper describes a compact Modulation Transfer Function Analyzer for long focal length, infinite conjugate optical systems testing. It uses a 12-inch aperture collimating off-axis parabola and two beam-folding mirrors. The analyzer scans the line spread function, produced by the optical system under test, with a mask having a sinusoidal transmittance grid which varies as a function of the rotation angle. The transmitted modulated flux generates an AC output rep-resentative of the modulation transfer function, which is plotted on an X-Y recorder. A heavy cross-slide bench as-sembly on a granite base provides the required mechanical rigidity and accuracy.