Solutions
Magnification Ocular power x Objective lens
Focusing Microscope Being with lowest objective power (4x)
Use coarse focus to move stage
Refine focus with fine knob
Change to higher objective power
Adjust with fine focus only
Parfocal Microscope Image stays in focus while changing lenses
Field Diameter Mount ruler slide, convert millimeters to micrometers (M1 FD1 = M2
FD2)