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The Collaborative International Dictionary
Parfocal

Parfocal \Par*fo"cal\, a. [Pari- + focal.] (Opt.) 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. ``the convenience of a microscope with parfocal objective lenses''

Wiktionary
parfocal

a. Having multiple lenses that have corresponding focal points in the same plane