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Optics Terminology.
Glossary of Terms:
Achromatic Multi Coating
Is a multi-layer broad-band coating applied to all lenses through a vacuum evaporation coating process. This serves to reduce the surface reflection of the glass. Light transmission in Kahles rifle scopes, as a result of the multi coating process is approximately 99.4% per air-to-glass surface on average over the total spectral region.
Exit Pupil
The aperture that delineates the shaft of light rays coming out of the ocular lens. (=diameter of the objective lens / magnification, e.g. 56/8 = 7mm)
Eye Relief
Refers to the distance from the ocular lens to the viewers eye, at which the complete field of view is clearly visible to the observer.
Field of view
Is the width of a sector of terrain viewed at a distance of 100 yards for rifle-scopes or a distance of 1000 yards for binoculars.
Objective
The lens which is closest to the object being observed.
Ocular
The lens closest to the viewers eye.
Parallax
Is the difference in the apparent position of the reticle on the target image at different ranges. This is most visible when the eye is moved outside the center of a scope while viewing a target at other than the standard distance at which the scope has been preset to be Parallax Free. All Kahles scopes are set Parallax free at 100 yards.
Position of the Reticle
In a rifle scope the reticle can be positioned in the Objective (1St) image plane, or the Ocular, the (2nd) image plane. If the reticle is in the (1st) image plane of a rifle scope, the reticle will be magnified in direct proportion to an increase in magnification. If, however, the reticle is positioned in the (2nd) image plane, the image only will be magnified, not the reticle.
Range of Adjustment
Is the capability of a rifle scope's internal adjustment to move the point of impact of an intended bullet's impact on a target.
Reticle Adjustment
The precise click adjustment of the wind-age and elevation permits an exact correction of shot's point of impact on a target. Clockwise adjustment moves the point of impact 1/4" at 100 yards.
Resolving Power
The resolving power, or resolution, of a rifle scope is the capability to sharply reproduce, point for point, details of the object at a distance.
Transmission
Is a technical term referring to "light transmission". The degree of transmission is the ratio between incident light (entering the scope) and emerging light (leaving the scope). When comparing the transmission values of different scopes, make sure that the values indicated refer to the entire optical system, i.e. to all air-to-glass surfaces.
Twilight Factor
This is a measurement of the efficiency of a rifle scope in low light conditions. (=the Square-root of Magnification x Diameter of the Objective lens) From a purely mathematical standpoint, the higher the twilight performance factor, the better the scope can be in twilight conditions.
Variable optic
A variable optic permits the continuous selection of a subject at various magnifications.
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