|Commonly Used Phrases and Terms
system of a spotting scope reduces the size of a long optical path
and correct an inverted image.
Roof Prism System
prisms overlap and are aligned in a straight line with the lenses
allowing to have a slim construction.
Porro Prism System
objective is offset from the eyepiece offering greater depth
perception and a wider field of view.
standards of optical prisms are barium-crown (BAK-4) glass or
borosilicate (BK-7) glass. The BAK- 4 is a higher quality
glass that reduces light scattering, resulting in sharper and
OBJECTIVE LENS DIAMETER
second number in the reference (i.e. 20-60×60) indicates the
diameter of the objective lens or the front lens. The larger the
objective lens, the better the light transmission, thus the
ED (Extra Low Dispersion)
ED Glass is designed to provide precise optical
color correction. It is multi-coated to improve contrast and
transmission across the visual spectrum and provides reduced
Magnification is the number of times the object
being viewed is enlarged. The spotting scope is often identified by
two numbers, for example: 20-60×60. The first number indicates
the magnification or the power of the scope, expressed by the letter
“x”, for times. With this variable zoom power, that means that the
object being viewed appears to be 20 to 60 times closer than would
be seen with the naked eye.
coating processes on the lenses and prisms will determine the
brightness and the light gathering of a spotting scope, providing
higher contrast and brighter images. The types of coating
Coated - A single layer on at least one
Fully Coated - A single layer on all
air-to-glass lens surfaces
Multi-Coated - Multiple layers
on at least one lens surface.
Fully Multi-Coated - Multiple
layers on all air-to-glass surfaces.
usually with a turn-adjustable knob, that is used to focus the
spotting scope on the object being viewed.
FIELD OF VIEW (F.O.V.)
is the side-to-side linear measurement of the circular field seen
through a spotting scope. It is defined by the width in feet of the
area visible at 1000 yards, or in meters at 1000m. The higher the
magnification, the narrower the field of view.
CLOSE FOCUS DISTANCE
closest distance to the observed object that the spotting scope can
be used while retaining a sharp focus.
of the scope’s ability to distinguish fine detail and
This refers to
the size of the small disc of light that exits a spotting scope. To
determine the size, divide the objective lens diameter by the
power. For example a 20×60 spotting scope will have an exit
pupil of 3mm. (60/20=3)
This is the
distance a scope can be held away from the human eye and can still
observe the entire field of view. Long Eye Relief (LER) reduces
eyestrain and is more comfortable for eyeglass wearers.
can be O-ring sealed for complete waterproof protection, and
fogproof which means that they are nitrogen-purged to prevent
anti-fogging inside the optical surfaces. These models are able to
keep completely dry inside after immersion in water.