Macro lens:  A lens designed for taking close-up pictures.

Main light The principle source of light in a photograph, particularly in a studio setup, casting the dominant shadows and defining the texture and volume of the subject.  Also called key light.

Manual exposure:  A nonautomatic mode of camera operation in which the photographer sets both the speed and the aperture.

Manual flash:  A nonautomatic mode of camera operation in which the photographer controls the exposure by adjusting the size of the camera aperture.

Mat:  A cardboard rectangle with an opening cut in it that is placed over a print to frame it.  Also called an overmat.

Mat knife A short knife blade (usually replaceable) set in a large, easy-to-hold handle.  Used for cutting cardboard mounts for prints.

Matte:  Describes a printing paper with a relatively dull, non-reflective surface.  Opposite:  glossy.

Middle gray:  A standard average gray tone of 18 percent reflectance.  See also gray card.

Midtone:  An area of medium brightness, neither a very dark shade nor a very bright highlight.  A medium gray tone in a print.

Modeling light A small tungsten light built into some flash units.  It helps the photographer judge the effect of various light positions because the duration of flash light is too brief to be judged directly.

Mottle:  A mealy gray area of uneven development in a print or negative.  Caused by too little agitation or too little time in the developer.