A vision system for viewing the end face of product (64) mounted in a machine and which in use produces measurements relating to the area of the end face and of at least one constituent part of the product which is visible in the said end face. The system comprises means for illuminating a region containing the end face and scanning (78) means for producing a video signal from an image of the illuminated region. The region is illuminated consecutively using first one (50) and then the other (58, 60) of two strobed light sources.