Method and apparatus for particle measurement employing optical imaging

Abstract From the Canadian patent

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 …