Zirconium lamp - an arc lamp used in powerful enlarges and projectors.
Zoetrope - an early device for creating illusion of continuous motion. A sequence of still pictures was viewed so quickly through slits in a rotating drum, that the images appeared to merge.
Zone focusing - a method of focusing the lens so that the depth of field extends over a preselected range of distances.
Zone system - the method of determining exposure and development required for individual scenes, invented by Ansel Adams. It is based on analysis of subject luminosities in terms of ten gray tones, labeled zones 0 through X and previsualizing them as print densities. By measuring each subject luminance with a hand meter it is possible to determine how much the range of values must be contracted or expanded by negative development control to give the required values in the print.