See Surface Detail and 3-D with Stereomicroscopes

When we think “microscope,” we probably picture a standard, monocular, compound microscope with a substage light that is transmitted through a specimen to our eye. These scopes are ideal for looking at prepared slides of thinly sectioned biological tissues, blood smears, and pondwater specimens—any tiny thing that is flat and at least partly transparent. But, what about something that is lumpy and opaque, such as a rock, shell, spider, or flower? Or, something with an interesting surface texture, such as fabric, or bark, or a patterned feather?

A stereomicroscope is the right tool for viewing surface detail of solid specimens. These microscopes are excellent for younger students, who are relentless in finding items to examine. A stereomicroscope typically has both a light in the base and an upper light to illuminate the specimen from above. The magnification generally ranges from 10x to 40x—sufficient because the items being examined are already visible to the unaided eye and can be manipulated into position with fingers or forceps. Stereomicroscopes deliver a 3-dimensional image of the specimen. Because each tube follows a separate optical pathway, a person views the specimen with both eyes from slightly different angles. (In binocular versions of standard, high-powered biological microscopes, there are 2 eyepieces for comfort, but the light passes through only 1 objective lens, and the image remains 2-dimensional.) A stereomicroscope’s use of 2 pathways mimics the effect of the binocular vision of our own eyes (while magnifying). The focal depth and quality of detail will amaze your students and get them excited about viewing the microscopic world.

Tips for using a stereomicroscope

• Always begin viewing with the lowest magnification setting. This makes it easier to focus and to position the specimen properly.
• Most stereomicroscopes come with a selection of stage plates. For viewing a microscope slide or transparent object in a glass dish, use the clear or frosted stage with the bottom light on. With some specimens, more features are revealed if you try both bottom and top lighting.
• If viewing opaque objects, use the top light. Try the white stage for dark specimens and the black stage for light specimens.
• To view living specimens such as ants or termites, use a small plastic petri dish to keep them contained in the viewing area.
• When viewing living organisms with microscopes that use tungsten bulbs, use only the top light, if possible. The bottom light may overheat the specimens. If you must use the bottom light to see full detail, keep the viewing time short.
• If you are purchasing a new stereomicroscope, consider one that uses LED or fluorescent lighting rather than tungsten. Both types are more energy efficient and last longer than tungsten bulbs, and they produce very little heat.