Modern Lens Design, 2nd Edition

^* Although the microscope objective designs are shown here at our standardized focal length of 100 mm, they are of course intended for use at much shorter focal lengths, at which their aberrations are correspondingly smaller.

To avoid confusion regarding the parts of an objective, we will identify them by their position in an ordinary vertical microscope as top or upper and bottom or lower. The customary terminology for these are rear and front, respectively, but since microscope objectives are designed from long conjugate to short (the reverse direction of the actual light path), the designer’s raytracing front is the microscopist’s rear and vice versa.