A method for reconstructing optical properties of diffracting objects bathed in a liquid medium, using a reconstruction system comprising a spatially coherent light source and a matrix photodetector, the liquid medium being delimited by a transparent surface, the diffracting objects being in contact with the transparent surface, the reconstruction method comprising the following steps: - lighting the medium with the spatially coherent light source, - measuring, with the matrix photodetector, an intensity of at least one diffraction pattern transmitted by the lit medium in a vertical direction, the or each diffraction pattern corresponding to waves diffracted by one or more diffracting objects during lighting of the medium, - reconstructing the optical properties of the objects at a reconstruction height (Zr), according to a reconstruction algorithm, based on the measured intensity, characterized in that, during the reconstruction step, the reconstruction height (Zr) has a value strictly lower than that of the distance between the medium and the matrix photodetector in the vertical direction, preferably lower than 0.9 times said distance between the medium and the photodetector, more preferably lower than 0.8 times said distance, and during the reconstruction step, the reconstruction algorithm verifies the following equation: I x y ∗ h − Zr x y = e j 2 π − Zr λ 1 − a x y − e j 2 π 2 Zr λ. a ∗ x y ∗ h − 2 Zr x y where I represents the intensity measured by the matrix photodetector, x, y represent the coordinates in a plane perpendicular to the vertical direction, * designates the convolution product, Zr represents the reconstruction height, λ represents the wavelength of the light source, j represents the unitary imaginary number, a represents the complex opacity function of an object, a* represents the conjugated complex of a, and h z is defined by the following equation: h z x y = 1 jλz e j 2 π z λ exp jπ x 2 + y 2 λz. - lighting the medium with the spatially coherent light source, - measuring, with the matrix photodetector, an intensity of at least one diffraction pattern transmitted by the lit medium in a vertical direction, the or each diffraction pattern corresponding to waves diffracted by one or more diffracting objects during lighting of the medium, - reconstructing the optical properties of the objects at a reconstruction height (Zr), according to a reconstruction algorithm, based on the measured intensity, characterized in that, during the reconstruction step, the reconstruction height (Zr) has a value strictly lower than that of the distance between the medium and the matrix photodetector in the vertical direction, preferably lower than 0.9 times said distance between the medium and the photodetector, more preferably lower than 0.8 times said distance, and x, y represent the coordinates in a plane perpendicular to the vertical direction, * designates the convolution product, Zr represents the reconstruction height, λ represents the wavelength of the light source, j represents the unitary imaginary number, a represents the complex opacity function of an object, a* represents the conjugated complex of a, and h z is defined by the following equation: h z x y = 1 jλz e j 2 π z λ exp jπ x 2 + y 2 λz.