An optical system , intended to measure the bidirectional reflectance and/or transmittance distribution function BRDF (bidirectional reflectance distribution function), BTDF (bidirectional transmittance distribution function) and BSDF (bidirectional scattering distribution function) of a surface , reflecting and/or operating in transmission, of at least part of an object , the system comprising successively in the direction of propagation of the diffused light: - an aplanatic objective capable of projecting the image of an intensity diagram of the light diffused by the surface , reflecting and/or operating in transmission, onto an intermediate observation plane P downstream of the aplanatic objective , - a converging field lens downstream of the plane P, - an image pickup objective whose field angle is greater than or equal to the convergence angle of the beams of the diffused light emerging from the field lens, and - a video sensor , the aplanatic objective , the converging field lens , the image pickup objective and the video sensor being arranged so as to allow a first conjugation C1 between the surface , reflecting and/or operating in transmission, and the entrance pupil of the image pickup objective and a second conjugation C2 between an intensity diagram of the diffused light and the video sensor , characterized in that the aplanatic objective has an angular resolution comprised between 10° and a value strictly greater than 0°, and comprises at least two lenses arranged so as to correct the aperture aberrations of the aplanatic objective , the aplanatic objective having an aperture angle whose absolute value is comprised between 60° and a value strictly less than 90°, the aplanatic objective comprising at least one aspherical lens; the converging field lens being aplanatic, the first conjugation then being aplanatic. - an aplanatic objective capable of projecting the image of an intensity diagram of the light diffused by the surface , reflecting and/or operating in transmission, onto an intermediate observation plane P downstream of the aplanatic objective , - a converging field lens downstream of the plane P, - an image pickup objective whose field angle is greater than or equal to the convergence angle of the beams of the diffused light emerging from the field lens, and - a video sensor , the aplanatic objective , the converging field lens , the image pickup objective and the video sensor being arranged so as to allow a first conjugation C1 between the surface , reflecting and/or operating in transmission, and the entrance pupil of the image pickup objective and a second conjugation C2 between an intensity diagram of the diffused light and the video sensor , characterized in that the aplanatic objective has an angular resolution comprised between 10° and a value strictly greater than 0°, and comprises at least two lenses arranged so as to correct the aperture aberrations of the aplanatic objective , the aplanatic objective having an aperture angle whose absolute value is comprised between 60° and a value strictly less than 90°, the aplanatic objective comprising at least one aspherical lens; the converging field lens being aplanatic, the first conjugation then being aplanatic. <EOS>