ABSTRACT
Compound microscopes are different from simple microscopes in that their images are formed by two lens systems, the objective lens and the ocular, or eyepiece. The stereomicroscope and the comparison microscope are the two types of compound microscopes most often used by toolmark examiners. Although the theory and nomenclature discussed herein apply to any type of compound microscope, this work will concentrate on the stereomicroscope and the comparison microscope.3-12
In its simplest sense, a compound microscope is an amalgamation of two lens systems and a source of illumination. The first lens, known as the objective lens, forms the primary image of the specimen. The ocular then magnifies the primary image and projects it to the eye-point (or Ramsden circle), which is the area above the field lens of the ocular at which the pupil is positioned. Figure 2.2 is a simple diagram of a rudimentary
compound microscope used by toolmark examiners. In Figure 2.2 a source of illumination is directed toward the specimen at an oblique angle. The light interferes with the specimen. The specimen, a metallic surface, reflects the light toward the objective lens, which collects the light and forms a primary image of the specimen. The primary image is then magnified by the ocular or eyepiece and presented to the eye-point, or Ramsden circle. There are two types of compound microscopes used by toolmark examiners in their daily work: the stereomicroscope and the comparison microscope. The parts and adjustments of each type, as well as important aspects of image formation, are presented in this chapter.
