PART III: THE DISSECTING MICROSCOPE
6.5 Exercise 5 – Features of the dissecting microscope
1. Locate the dissecting microscope in your carrel or in the Central Study Area. Identify the major
features of the dissecting scope: stage (for specimen), eyepieces, objective lens, zoom knob, focusing knob, and light sources above and below specimen (Figure 2).
2. The dissecting microscope differs from the compound scope in many ways: a. Total magnification is much lower (maximum either 30 or 45 power). b. Objective lens is equipped with a “zoom” adjustment. c. Two ocular lenses give a stereoscopic (3-D) view of the specimen. d. Only one focus adjustment knob. e. Longer “working distance” (between specimen and objective lens). Figure 2: The Dissecting Microscope
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3. Why do some microscopes have two eyepieces? Dissecting microscopes always have two eyepieces, which are connected to two separate objective lenses. The two separate optical systems work in parallel to give a stereo, 3-D image. Although some compound microscopes also have two eyepieces, both eyepieces are connected to the same objective lense and so never can produce a 3-D image. In a compound microscope the second eyepiece simply serves to reduce eyestrain during prolonged use.
6.6 Exercise 6 – Use of the dissecting microscope.
1. Illumination (lighting) of the specimen can be from above or below. Since the e is printed on
translucent paper, it should be clearly visible under both lighting conditions. So examine an opaque object instead — like the leg of an insect. Is the specimen more easily seen using reflected light (with the light source above the specimen) or transmitted light (with the light source under the specimen)?
2. Total magnification of the dissecting microscope can be calculated by multiplying the power of the
eyepiece engraved on the side of the eyepiece by the power of the objective (zoom) lens read from the dial on the zoom control knob. First set the zoom lens so that the “e” appears as small as possible and calculate total magnification. Then set the zoom so the “e” appears as large as possible and calculate the highest magnification.
3. How does the orientation of the image you see compare with the actual letter “e” as you move the
slide around. Enter your observations in the right column of the Table 1.
Power setting Power of eyepiece (ocular lens) x
Power of zoom objective lens =
Total magnification
Minimum zoom
Maximum zoom
4. Summarize the appearance of the letter e in the four cases you observed: Naked eye Compound scope Mirror Dissecting scope