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.