Marking Optical Components - Continued
Marking Components for Light Travel and Deviation. The marking of components for light travel, deviation in
prisms, and focal length in lenses is usually done by the manufacturer. To help the repair person understand what these
markings represent, a brief description is as follows:
Variations in lenses from the intended focal length represents the only characteristic usually noted on a
lens. The lens should be marked on its unpolished surface in a plus or minus thousandths of an inch,
according to whether its focal length is longer or shorter than that desired or specified, as shown in
In prisms, such as binocular prisms, the direction of deviation is indicated such as 2 oclock, 5 oclock, or
6 oclock, followed by the amount of deviation such as 2 minutes, 3 minutes, or 4 minutes. For example
a prism marked 5-3 indicates that the prism has a 3 minute deviation at 5 oclock. Light travel, whatever
the method used for its determination should be noted as plus or minus in relation to the ideal condition,
and should be marked in thousandths of an inch such as .007 or .005 on the prism as shown in figure 9-
Inspecting Optical Components.
General Inspection. All optical components should be inspected by the repair- person for defects before they
are installed in an optical system. All components will be inspected according to the criteria contained herein. Any
component not meeting these standards must be reground and repolished. Should the defects of the component be
extensive, the component should be discarded.
Definitions of Defects:
Chip. An indentation, usually irregular in shape, in a glass surface where a small piece of the glass
surface has been chipped out, struck, or flaked off. A small crack which can be removed by honing.
Condensation (Moisture). Visible particles of water or visible staining due to the presence of water on
Dig. A small, very short scratch in the glass surface. The size of the dig can be measured by
comparison with the established dig standard.
Dirt. Visible particles or specks of foreign matter, such as dust, soil, paint flakes, and sand adhering to
the glass surface.
Fingerprints. A visible impression upon the glass surface of the arches, loops, whirls, or composites of
Fractures. A crack or break on the exterior of the component and extending well into or all the way
through the glass diameter or thickness.
Inclusions. A term used to denote the presence, within the body of the glass, of extraneous or foreign
matter. Bubbles, for example, are a gaseous inclusion.
Lint. Particles of cloth or paper fibers adhering to the component surface or entrapped between the
cemented component surfaces.
Change 2 9-20