Spotting Scopes - Tech Talk

Coated Optics

Coatings on lens surfaces reduce light loss and glare due to reflection for a brighter, higher-contrast image with reduced eyestrain. Bushnell® riflescopes are coated with a microscopic film of magnesium fluoride. More coatings lead to better light transmission.

Exit Pupil

The size of the column of light that leaves the eyepiece of a scope. The larger the exit pupil, the brighter the image. To determine the size, divide the objective lens diameter by the power (a 4x32 model has an exit pupil of 8mm).

Eye Relief

The distance a spotting scope can be positioned away from the eye and still present the full field-of-view. Extended or long eye relief reduces eyestrain and is ideal for eyeglass wearers.

Field-of-View (F.O.V.)

Field-of-view is the side-to-side measurement of the circular viewing field or subject area. It is defined by the width in feet or meters of the area visible at 1000 yards or meters. A wide field-of-view is better for following fast-moving action or scanning for wildlife. Generally, the higher the magnification, the narrower the field-of-view.

Magnification (Power)

Spotting scopes are often referred to by numbers separated by an "x". For example: 15–45x60. The first number(s) indicate the power or magnification of the spotting scope. With a 15–45x60 variable power spotting scope, the object being viewed appears to be 15–45 times closer than you would see it with the unaided eye.

Multi-Position Eyepiece

Bushnell's exclusive multi-position eyepiece is available on our 787360 Spacemaster® model. This revolutionary eyepiece features an infinite number of viewing positions between straight-thru and 90 degrees – providing flexibility for viewing comfortably in any situation.

Near or Close Focus

The closest you can be to an object and maintain visual clarity.

Objective Lens Size

The number after the "x" in the formula: (15–45x60) is the diameter of the objective or front lens. The larger the objective lens, the more light that enters the spotting scope and the brighter the image.

RainGuard® HD

Bushnell's permanent, patented, hydrophobic (water-repellant) lens coating prevents fogging by causing condensation from rain, sleet, snow or even your own breath to bead up into much smaller droplets than on standard coatings. Smaller droplets scatter less light which results in a clearer, brighter view. Now the hunter won't miss the shot of a lifetime because of rain or accidentally breathing on his eyepiece.

Porro Prism System

The objective or front lens is offset from the eyepiece. Porro prism scopes provide high performance and generally offer a wider field-of-view.


The use of a spotting scope for long range wildlife photography. This is typically done by mounting a compact digital camera behind the scope's eyepiece with a bracket or other accessory, but an SLR camera body may be used instead via a dedicated mounting system (if the scope offers that option).

Prism Glass

Most optical prisms are made from borosilicate (BK-7) glass or barium crown (BaK-4) glass. BaK-4 is the higher quality glass yielding brighter images and high edge-to-edge sharpness.

Prism Systems

The prism system turns what would otherwise be an upside-down image right-side-up.


Resolution, or definition, is the ability of a scope to distinguish fine detail and retain clarity.

Roof Prism System

The prisms overlap closely, allowing the objective lenses to line up directly with the eyepiece. The result is a slim, streamlined shape in which the lenses and prisms that magnify and correct the image are in a straight line.

Folded Light Path

A special optical configuration using a combination of lenses and mirrors to create a total scope length much shorter than the total focal length of the system. This provides a compact design yielding long focal length performance.

Types of Coatings

Coated – A single layer on at least one lens surface.
Fully Coated – A single layer on all air-to-glass surfaces.
Multi-Coated – Multiple layers on at least one lens surface.
Fully Multi-Coated – Multiple layers on all air-to-glass surfaces.


Some scopes are sealed with O-rings and nitrogen-purged for waterproof and fogproof protection. These models are able to withstand complete immersion and remain dry inside.