The invention relates to image analysis of dark field images obtained at low magnification below 10:1. Image analysis of dark field images obtained at low magnification can be combined with analyzes of images obtained in respect of the same section of a sample and same magnification but with other techniques such as fluorescent microscopy. The system and method can be used e.g. for particle counting, particle size measurement, particle size distribution, morphology measurement, where the particles can be cells and/or cell parts. The invention also relates to a compact dark field light source unit, a system or apparatus including a microscope which by itself is compact and comprises the mentioned dark field light source unit.