Page 61 - Fundamentals of Light Microscopy and Electronic Imaging

44 LENSES AND GEOMETRICAL OPTICS

Figure 4-1
Geometrical optics of a positive lens. (From Hecht, 1998.)

For any given lens there are two principal planes: one each for the front and back
surface of the lens. For the special case of a thin biconvex lens, the two principal planes
are coincident in the middle of the lens. Microscope objectives contain multiple lens ele-
ments, some of which may be united with transparent sealing compound to make a com-
plex thick lens. The principal planes of thick lenses are physically separated, but their
locations can be determined by ray tracing. Most lens elements used in microscope
optics are ground and polished with spherical curvatures.

Double Plano Convex
convex convex meniscus
Positive lenses

Double Plano Concave
concave concave meniscus
Negative lenses

Figure 4-2
Examples of positive and negative lenses.