The eyepiece is basically a projection lens system. There are three types generally used in light microscopy. The most common is the Huygenian type. This eyepiece is used with low and medium magnification and is esigned to project the image into a human eye. Some of these eyepiece will have a long eyepoint, the spot there your eye should be, so you can focus with your glasses on. If you suffer from stigmatism you should ware your glasses while using the microscope. If you are near or far sighted then you can adjust the eyepiece for your personal correction using the diopter corrector and leave your glasses off. The second type of eyepiece is the compensating eyepiece and is generally used with apochromate or flat field objectives. These provide superior image quality. The third type is the photo eyepiece. These are designed to project a corrected image onto film plane in a camera. These are generally considered the finest of eyepieces. All eyepieces will have a relative magnification written on the side of the barrel. They range in magnification from 2.5X to 15X with the lower magnifications used with the photo eyepiece.

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.