Multiple Images in Reflecting Microscopes

The normal image of a reflecting microscope is formed by a single reflection at each mirror surface. However, other images are possible ; higher order images formed by two or more reflections at each surface, and a zero order "image" which is the object itself, if there is an unobstructed light path through the system. In a mirror system possessing central obscuration of the pupil, this unwanted light usually does not reach the axial image point, but it may give rise to a spread of light across the outer parts of the field, so reducing the contrast. The effects of these extra images are most noticeable when the objective is used in reverse as a condenser.