Eyepieces can be adapted for measurement purposes by adding a small circular disk-shaped glass graticule (or reticle) at the plane of the field diaphragm of the eyepiece. Graticules usually have markings, such as a measuring rule or grid, etched onto the surface. Because the graticule lies in the same plane as the field diaphragm, it appears in sharp focus superimposed over the image of the specimen. Eyepieces using graticules must contain a focusing mechanism (usually a helical screw or slider) that allows the image of the graticule to be brought into focus. Several typical graticules are illustrated in Figure 5 below.
Manufacturers often produce specialized eyepieces, often termed photo eyepieces, that are designed to be used with photomicrography. These eyepieces are usually negative (Huygenian type) and are not capable of being used visually. For this reason, they are typically called projection lenses. A typical projection lens is illustrated in Figure 7 below.
Camera systems have become an integral part of the microscope
and most manufacturers provide photomicrographic attachment cameras as
an optional accessory. These advanced camera systems often feature motorized
black boxes that
store and automatically step through film frame-by-frame
as photomicrographs are taken.