Abstract: A system and method for measuring small particles suspended in a fluid are disclosed. The system employs optical imaging using diffraction enlargement. A sample of small particles illuminated by a light source is imaged onto a pixel array of detector elements using an imaging optical system having a reduced magnification not sufficient for forming a large enough image of a smallest particle of interest. A low-aperture imaging optics with NA<0.05 is used to add diffraction enlargement to the image corresponding to at least 5 pixels to enable accurate measurement of images of smallest particles of interest, and to increase an optical sampling volume. Suitably programmed processor is used for determining at least a pixel count for each of the diffraction-enlarged images, and for generating a number, size or distribution of particles accounting for pre-determined diffraction enlargement of particle images of different sizes. The method enables analysis of large samples of small particles in one measurement.

Abstract: A method for determining a distribution of a parameter of a particle population is disclosed whereby the following steps are performed: a) detecting on a pixel array of elements a plurality of images of the particles; b) determining a number of pixels in the form of a pixel count corresponding to each of the plurality of images of particles; c) obtaining a plurality of weighting factors which relate values of the parameter to different pixel counts; and, d) utilizing the plurality of pixel counts and the weighting factors to determine the distribution for the parameter of the particle population. The method depends on the facts that the total population to be analyzed contains many particles and is uniformly distributed, over many frames, throughout the optical sampling volume, and that even when substantial uncertainty exists on the parameter value corresponding any individual image, the statistical information which is obtained from many images may be used to provide accurate distributions.