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Glossary of Terms Used in the Optical Characteristics Table
Working distance (WD)
: The distance from the top of specimen and the front lens of objective.
Number of aperture (NA) : Important figure determining the objective characteristics (resolution, focal depth and bright-
ness).
Resolution ............. Increases in proportion with the NA.
Focal depth ......... Decreases in proportion with the NA.
Brightness ............. Proportional with the square of NA (comparison under the same magnification).
Resolution
: The limit that an objective can identify the images of two points that are close to each other,
expressed as the distance between the two points on the specimen.
Depth of focus
: The maximum depth of the specimen at which the entire specimen can be brought into focus
simultaneously. This value increases when the aperture iris diaphragm is narrowed and de-
creases when the objective NA is increased.
Field number
: The diameter of the image area that can be observed through the eyepieces, expressed in mm.
Field of view
: The diameter of the area observable on the specimen, expressed in mm.
