[医] 正焦点的

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''
[Webster 1913 Suppl.]