Microscope Activities, 36: 3-D Photomacrography

In the past, Hooke College of Applied Sciences offered a microscopy workshop for middle school and high school science teachers. We thought that these basic microscope techniques would be of interest not only for science teachers, but also for homeschoolers and amateur microscopists. The activities were originally designed for a Boreal/Motic monocular microscope, but the Discussion and Task sections are transferable to most microscopes. You may complete these 36 activities in consecutive order as presented in the original classroom workshop, or skip around to those you find interesting or helpful. We hope you will find these online microscope activities valuable.

EXPERIMENT 36 • 3-D Photomacrography

Goal

To make and view 3-D low-power photographs using a stereomicroscope.

Level

Basic

Materials Needed

Any low-power stereomicroscope, and any film or digital camera. Optional: an inexpensive stereoscope.

Procedure

Select any specimen you wish to record in 3-D, and focus on it using a stereomicroscope, being careful to select the magnification, and to arrange the lighting so as to optimize the image quality.

Attach a camera (see Experiment 18) to the left eyepiece of the stereomicroscope (some photomicrographic cameras have a built-in eyepiece that takes the place of the microscope’s eyepiece).

Make sure the sample is in focus by checking the LCD screen on the digital camera, or by focusing visually—leaving eyeglasses on, if you wear them—before attaching a film camera, and make the left-side exposure (Figure 36-1).

Move the camera to the right eyepiece of the stereomicroscope, check the focus, and make the right-side exposure (Figure 36-2).

Label the two resulting prints “left” and “right,” according to which side they were made on, and arrange them so that similar structures on the two prints are 65 mm apart—you may want to trim the blank edge of one of the photos (Figure 36-3). Arranged photos of this kind are called a “stereo pair.”

View the resulting stereo pair either by free-viewing, or by using a stereoscope to see the original specimen in 3-D (Figures 36-4, 36-5, 36-6 and 36-7).

Discussion

With normal vision involving two eyes, we perceive objects in three dimensions with adequate depth perception, except when the objects are very far away. The reason we perceive depth in three-dimensional images is because each eye is seeing the object from a slightly different angle, and the two separate images are fused in the brain to give the sense of depth. More specifically, the average distance between the eyes of humans is 65 mm. The nearest distance for comfortable reading is 250 mm (about 10 inches). We can construct a right triangle by taking half of the interpupillary distance (65 mm ÷ 2 = 32.5 mm) and the 250 mm, and calculating the angle from the tangent (32.5/250 = 0.13 = 7.4°); i.e., about 15° (2 x 7.4°) included angle using both eyes for an object 10 inches away. Stereomicroscopes are, in effect, two separate microscopes—one for each eye—arranged so that they make a total included angle of 15° to the object. (Actually, most stereomicroscopes are constructed with a somewhat larger angle, so as to produce a hyper-stereoscopic effect for flatter objects).

In the Greenough-design microscope, the two separate microscopes, with their two separate objectives, are readily apparent, but even with the common main objective (CMO) stereomicroscope, the principle is the same; it is just that one-half of the front lens is used for each eye. So, making a photo through only one side of the stereomicroscope results in a flat image, just as when you close one eye; making two photos—one through each eyepiece—results in a stereo pair, in which each photo represents the view of the specimen from two different angles.

The problem comes in the proper viewing of a stereo pair; each of the two photos must be presented separately to the appropriate eye—the left-side photo to the left eye, and the right-side photo to the right eye—so that the separate images may be fused in the brain to achieve the sense of depth.

Viewing Stereo Pairs

Many people—especially youngsters—have the ability to free-view, meaning they have the ability to maintain infinity focus while looking at the stereo pair; they do not focus directly on the stereo pair, but rather, through it. Many posters, framed pictures, and entire books of such 3-D images have been popular in recent years, much to the frustration of onlookers who cannot free-view. The ability to free-view comes easily and naturally to some people, and can be an acquired skill through practice. A few people never seem to get the hang of it; it is sort of like staring off into space; that’s when the eyes relax their close focus, and focus parallel to infinity.

For those who cannot free-view, there is always the stereoscope, which is an optical device made for viewing stereo pairs. Do not confuse “stereomicroscope” with “stereoscope!” They are two different instruments, even though you hear people incorrectly refer to the stereomicroscope as a “stereoscope.” A stereomicroscope is used to make stereo pairs, which are viewed with a stereoscope. In writing, however, “stereo ’scope” is often used as an abbreviated form for stereomicroscope. A cardboard stereoscope that costs less than $2.00 is illustrated in Figure 36-4. It has built-in prismatic lenses made of plastic that force infinity focus; it comes collapsed, and fits folded in a cardboard envelope. For use, it is expanded from its folded position, and held before the eyes to view a stereo pair, as illustrated in Figure 36-5. Still another very inexpensive, folding plastic stereoscope with built-in plastic lenses is illustrated in Figure 36-6. A war-surplus stereoscope with glass lenses in metal frame with adjustable interpupillary distance is illustrated in Figure 36-7. This stereoscope was made for viewing aerial photographs taken from two different positions. In all of these stereoscopes, each eye is diverted to see only the photograph made to be seen by that eye, so that no special skill is needed to fuse the images; the brain easily fuses the separately-presented images.

Figure 36-8 is a stereo pair of the Maple Bladdergall Mite Galls (Vasates quadripedes), arranged with similar structures 65 mm apart for you to practice free-viewing, or to view with a stereoscope.

Task

Make stereo pairs using any stereomicroscope and any film or digital camera, arrange the resulting two prints so that identical structures are 65 mm apart, and view the 3-D image either by free-viewing, or by viewing with the aid of a stereoscope.

References

Delly, John Gustav and Brown, John A. (1980) Light and SEM Stereomicrography. “Technology Trends” column in Optical Spectra 14 (12) 32, 34-38.

Ferwerda, Jac. G. (1982) The World of 3-D; A Practical Guide to Stereo Photography. The Netherlands Society for Stereo Photography, 306 p.

Judge, Arthur W. (1926) Stereoscopic Photography; Its Application to Science, Industry and Education. Chapman & Hall, London, 240 p.

McCrone, Walter C. (1965) Stereophotomicrography Using the Tilting Stage. The Microscope 14 429-439.

Russ, John C. (2005) Assembling Stereo Anaglyph Images with Photoshop.