An object is brought into focus using the 10x objective lens. When the 40x objective lens is moved into position, only a minor adjustment using the fine focus adjustment is required to bring it clearly into focus
What is the term used to describe lenses with this feature?
a. Parcentric
b. Achromatic
c. Plan-achromatic
d. Parfocal
ANS: D
When objective lenses are parfocal, only a minor adjustment using the fine focus knob is required to bring an object into focus when moving from one lens to another. Achromatic and plan-achromatic describe how (or if) a lens corrects for the curvature in a field, thus whether or not only part of or an entire field is in focus at the same time. Parcentric means that an image in the center of a field remains close to the center when a different objective lens is brought into position.
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