Brownian motion correction method for particle measurement

A particle measuring method comprising:

• irradiating a sample flowing through a flow passage with irradiation light;
• condensing light scattered from a particle contained in the sample passing through a detection region that is formed in a prescribed section of the flow passage by irradiation with the irradiation light, at a position obtained by extending the prescribed section in a flow direction of the sample;
• capturing, by a camera, the condensed scattered light at a prescribed frame rate;
• calculating movement amount of the particle due to Brownian motion in two-dimensional directions on a basis of captured plural frame images;
• correcting the calculated movement amount using correction values that were obtained in advance so as to correspond to each of defocus positions of frame images captured the condensed scattered light to correct for a magnification error that occurs due to defocusing at condensing the scattered light;
• determining a particle size of the particle on the basis of the corrected movement amount;
• outputting a result of the determination of the particle size to one of a display screen, a printer, a storage unit, and a network,
• wherein the correcting the calculated movement amount comprises using a correction map that stores the correction values corresponding to respective positions on a light receiving surface of the camera, and
• wherein the correction values are obtained by optical simulation software that calculates magnification errors for predetermined object heights at different defocus positions in the flow direction.