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  • Spotting Scopes 101

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  • spotting scopes

Spotting Scopes 101

Nikon Prostaff 5 20-60x82mm Zoom Spotting Scope Nikon Prostaff 5 Zoom Spotting Scope

A Spotting scope is an optical instrument used to view distant objects primarily on land - therefore optimized for terrestrial observations. Most spotting scopes are look and work just like small telescopes with refractor, Maksutov, or catadioptric optical design. Normally spotting scopes have 50mm to 80mm objective lens and magnification anywhere from 15x to 60x, but there are more powerful spotting scopes with higher magnification and larger objective lens to 90mm and up.

Coatings on lens surfaces reduce light loss and glare due to reflection, resulting in a brighter, higher-contrast image with reduced eyestrain. Many spotting scopes are coated with a microscopic film of magnesium fluoride. More coating leads to better light transmission. ED (Extra Low Dispersion Glass) in our best spotting scopes provides exceptional color correction and razor sharp images for serious nature and bird watchers, and it virtually eliminates chromatic aberration usually seen during planetary and lunar viewing - perfect for astronomical and terrestrial observations as well! High Quality spotting scopes feature the best coating available. HD (High Definition) spotting scope glass helps to eradicate the slightest chromatic zonal aberrations and contributes to a more faithful color image and normally recommended for digiscoping.

Types of Coatings

Barska Tactical 11-44x50 Angled Fully Multi-Coated Waterproof Spotting Scope Barska Tactical 11-44x50 Angled Fully Multi-Coated Spotting Scope

Coated - A single layer on at least one lens.

Fully-Coated - A single layer on all air-to-glass surfaces.

Multi-Coated - Multiple layers on at least one lens and all surfaces are coated at least once.

Fully Multi-Coated - Multiple layers on all : air-to-glass surfaces.

Exit Pupil

The exit pupil refers to the size of the column of light that exits a spotting scope. The larger the exit pupil, the brighter the image. To determine the size, divide the objective lens diameter by the power (a 15x45 model has an exit pupil, or useable light, of 3mm).

Eye Relief

The distance a spotting scope can be held 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.

Folded Light Path

A combination optical configuration using 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.

Spotting Scope Magnification (Power)

Spotting scopes are often referred to by two numbers separated by an "x". For example: 15-45x60. The first number is 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. We always recommend a quality tripod to hold the spotting scopes steady!

Near or Close Focus

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

Objective Lens Size

The second number 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.

Prism Glass

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

Prism Systems

Bushnell ImageView Digital Camera Spotting Scope Bushnell ImageView Digital Camera Spotting Scope

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

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

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.

Porro Prism System - The objective or front lens is offset from the eyepiece. Porro prisms provide greater depth perception and generally offer a wider field of view.

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