Digital Stereo Microscopes: Letting the Computer Help
Two Dimensional Vision
Traditional (or compound) microscopes may have one or two eyepieces; those with two are much easier on the eyes of researchers. It is less strain to look at something with both eyes, rather than with one squinted closed to eliminate distractions or, after much practice, left open and ignored while concentrating on the other.
Such a scope only has a single light-path; even if it is split into two images, it is still a visually flat 2-D image, and there is very little sense of depth. These are ideally suited to looking at things on the cellular level.
They can reach extreme magnification values. Typically, these have the standard 10x (ten power) eyepiece, or a swappable 15x eyepiece, for those occasions where you need a little more “Oomph” to see some finer details. Combined with a 100x objective lens, those two would provide the maximum practical magnification of up to 1500x for a compound light-based microscope.
More often, you will see a single or double eyepiece model with what appears to be an additional eyepiece pointing straight up. This is usually designed for attaching a camera for documentation or teaching purposes. While still used quite often nowadays, this older style was the precursor to the modern digital microscope, which we will address below.
Seeing in Stereo
Stereo microscopes have two distinct light paths, created by having two paired microscopes conjoined. They are slightly offset, with light paths designed to intersect at the observation point on the viewing stage. This creates the angle of separation that our eyes are used to.
You should note that a stereo microscope, sometimes called a stereoscope, also has a more descriptive name for its original function—it is called a Dissecting Microscope. It is used to study larger items, such as insects, archeological finds, mineral specimens, and more.
Don’t let its lower magnification power fool you about its capabilities. It is highly useful for many specialized purposes. It also can focus well above the stage designed for holding samples, since it is intended to look at larger objects. This is the sort often used for microsurgery, too. If an optic surgeon is working on you, most of us would agree that s/he ought to be able to see how far an instrument is from your eye!
Another difference is that unlike a compound microscope, the stereoscope illuminates its subject from above, so images are seen by reflected light rather than transmitted light. Seeing in stereo gives magnificent depth perception. As an experiment, try covering one eye and attempting to touch a small object on your desk with a fingertip—you will almost certainly miss. Stereo vision is essential to judge size and distance.
Another way to experience this is by holding a finger half an arm's length, from your eyes, and looking at a more distant object. Alternately, open and close each eye a few times, and while you’re focused on the farther object, your finger will appear to jump back-and-forth.
You’ll also notice if you study your finger while alternating eyes, that your right eye will see more of the right side of your finger as it curves away, and the left will see more of the left side. Your brain uses these missing bits from opposite eyes to calculate depth and distance.
|These scopes take the whole process one step further. They allow us to send the image to an auxiliary high-resolution screen, eliminating the need for using the eyepieces at all except for some extremely specific scrutiny of very fine structures. Some scopes eliminate the eyepieces, while others retain both viewing systems.|
Using a screen makes it much easier for young students to see the results they are getting more quickly, which encourages interest. Screens are also highly useful for showing information to large groups for teaching purposes.
Of course, what can be sent to a screen can also be sent to a computer—and once the image data is in there, we can do all sorts of things with coloration, brightness, enhanced resolution, contrast, and blending different views into one composite image.
A New Trick
For example, one brand new technology called cryo-SR/EM allows us to combine the results of a high-power optical-scan using super-resolution fluorescence, which provides remarkable detail, and the structural data from an electron microscope scan. This is taking place through the Howard Hughes Medical Institute’s (HHMI) Janelia Research Campus, in Virginia, consequent to their cutting edge development.
This technique provides a detailed three-dimensional view of a cell’s very crowded inner workings. The trick is that the cell is frozen under high pressure, so ice crystals don't form in a jagged, "pointy" manner and pierce the cell’s walls, destroying it. This completely preserved cell can then be imaged using fluorescent molecular tags.
Immediately afterward, the cells are embedded in resin, placed inside the vacuum chamber of an electron microscope, and an ion beam ablates the surface away so the electron microscope can image layers which can then be assembled into a moving image, (such as the quick & brief version) shown here. Once the end is reached, and the image is reversed, false color can be overlaid to identify many of the important structures.
It’s important to remember that all of this is going on in just one cell (there are two examples in the video), and a researcher would look at each individual frame. While this little “movie” is useful for gross studies and informing the public, the real benefit is the amazing detail that is available with this technique that we have never had available before.
Stereo scopes vastly improve our ability to understand the relative size of objects from the world of the very small. Digital scopes allow us to send images to a computer where we can tune the image to reveal less-obvious details.
Together digital and stereo techniques reveal aspects that would be invisible to, or unseeable by, the more conventional compound microscope. In the same way that you wouldn’t attempt to turn over the soil in your garden using a dinner fork, we have to appreciate the different tools we have available for different jobs.