parfocal

Microscope objectives that are mounted in such a way that changing objectives does not put the specimen out of focus are parfocal.

Parfocal

Par·fo'cal adjective [ 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.
Found on http://www.encyclo.co.uk/webster/P/23

Parfocal

• (a.) 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.
Found on http://thinkexist.com/dictionary/meaning/parfocal/

Parfocal

A microscope that is “parfocal” is one which, if it is in focus with one objective, when the objective is rotated, will remain in focus.
Found on http://www.greatscopes.com/glossary.htm
No exact match found