A microscope is an instrument that produces an accurately enlarged image of small objects so that the user can see things on a larger scale. The word microscope comes from the New Latin word microscopium, which comes from the the combining form micr-, meaning “small” and scope, meaning “an instrument for viewing.” The word monocular is from Late Latin monoculus, which means “having one eye.” Thus, a monocular microscope is an instrument for viewing small things through a single lens.
Microscopes are classed both by the number of eyepieces, as well as by the way in which the image is enlarged. While a monocular microscope is made for one eye, binocular and stereo microscopes are made for both eyes. Trinocular microscopes are binocular or stereomicroscopes with a third eyepiece, which may either be for a second person to share the view or in order to affix a digital camera or video camera to the third eyepiece in order to create a lasting record of what was seen.
A monocular microscope can have single or compound lenses. Simple microscopes—those with a single lens—are only available as monocular microscopes. Single lens monocular microscopes include the various types of lenses that are also known as magnifying glasses. Also included are jeweler’s lenses or loupes, and reading glasses. Many people are not used to thinking of these as microscopes, but that is how they are classified.
Since various types of image distortion occur with a single lens, their uses are limited. One type is chromatic aberration, which distorts color. Another is spherical aberration with distorts the focus.
A compound lens magnifier is different from a compound microscope. A compound lens magnifier is one single array of simple lenses with a common access. The use of a compound lens is attractive because it can correct some of the single lens aberrations, as well as magnify at a higher power, and being handheld, it has the same flexibility as a magnifying glass or loupe. It is, by nature, a monocular microscope.
Although a compound microscope has a minimum of two lens arrays, which helps to increase the maximum magnification possible, it can still be a monocular microscope if it only has one eyepiece. One of the arrays is the ocular, and this is the lens array that the viewer looks through. The other lens array is the objective, which is positioned near the object that is being viewed.