Definitions for "Parfocal"
With the lower focal points all in the same plane; -- said of sets of eyepieces so mounted that they may be interchanged without varying the focus of the instrument (as a microscope or telescope) with which they are used.
A lens design such that allows specimens to remain focused at different magnification powers.
a term used describing the property of a microscope where the subject stays in focus when the objective lenses are changed. Less then 1/2 of a revolution from the fine adjustment is usually acceptable.