APERTURE, ANGULAR
The angle (or cone) of light rays capable of entering the front lens of the objective from a
point in the object. By increasing the angular aperture of an objective, more light rays from
the specimen can be taken in by the lens; hence the resolving power is increased.
COMPOUND MICROSCOPE
A microscope having a primary magnifier (the objective) and a second (the eyepiece) to both
conduct light, amplify magnification and convert the image into a field of view easily seen by
the human eye.
COVER GLASS
Thin glass cut in circles, rectangles or squares, for covering the specimen, usually a
thickness of 0.15 to 0. I7mm. The majority of specimens should be protected by a cover
glass, and must be covered when using 40X or 100X objectives.
DEPTH OF FOCUS
The ability of a lens to furnish a distinct image above and below the focal plane. Depth of focus
decreases with the increase of numerical aperture or with the increase of magnification.
EYE POINT OR EYE RELIEF
The distance from the eyepiece lens to your eye where a full field of view can be seen.
FIELD OF VIEW
The area of the object seen when the image is observed. It may range in diameter from several
millimeters to less than 0.1mm.
FOCAL LENGTH
Parallel rays of light after refraction through a lens will converge to a focus at the focal point.
The distance from the optical center of the lens to the focal point is the focal length.
NUMERICAL APERTURE (NA)
A measure of an objective’s light gathering capabilities. The concept may be compared to the
F-valve in photographic lenses. Generally speaking, objectives with N.A. values of less than
1.00 are "Dry" objectives. Values of 1.00 or greater require oil as a medium. Please note that
condensers are part of the optical system and are also assigned an N.A. value. That value
must be at least as high as that of the highest objective used.
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SERIES
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IMPORTANT MICROSCOPY TERMS
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