 Microscopes were illuminated by gas lamps, mirrors or other primitive light sources, resulting in an uneven specimen illumination unsuited for producing good quality photomicrographs using the slow-speed emulsions available at the time.Over the course of his work for his doctorate degree, Köhler developed a microscope configuration that allowed for an evenly illuminated field of view and reduced optical glare from the light source.It involved a collector lens for the lamp that allowed the light source to be focused on the front aperture of the condenser.