We describe an experiment aimed at diffraction-limited imaging of astronomical sources in the 2-5/micron range. It is based on a rotation shearing interferometer that extracts the complex degree of coherence of the wavefront directly in the pupil plane. Interference fringes are produced by a Michelson interferometer in the image of the telescope pupil. They are scanned through the zero optical path difference faster than the deformations produced by atmospheric turbulence. The 2D interferograms are recorded with an infrared camera located at the recombined pupil image. For each spatial frequency, the modulus, and the phase of the Fourier transform of the object intensity distribution are derived from these interferograms. The main advantage of this technique is its high constant transfer function that makes it independent of seeing variations and instrumental aberrations. We describe the experimental set-up and discuss some model-based simulation results which illustrate the operation of the interferometer. We present astronomical data and derive the performances of rotation shearing interferometry for diffraction-limited observations of infrared astronomical objects.