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This page is a simple guide for those looking to buy a scope.
A spotting scope is a device that is used to view distant objects especially that on land. It is similar in construction and function to an astronomical telescope with a few minor changes. Usually spotting scopes provide a magnification of 15X to 60X and the size of the objective lens varies from 50mm to 80mm. However, high quality spotting scopes with objective lens size of up to 90mm are also available.
A coating on a spotting scope not only makes it perform better and deliver better images but also lengthens its lifespan. A coating on the lenses decreases the light reflection to a minimum thereby producing better images. The kind of coating depends on the quality of the spotting scope. A good spotting scope has lenses made of ED glass that eliminates all possibilities of chromatic aberrations. The coating can be of a single layer on the lenses or on all the external surfaces. The coating can also be multiple layered on the lenses or on the external surfaces.
The exit pupil is the size of the beam of light that leaves the spotting scope lens. The larger the size of the beam the brighter is the resultant image. To find the exit pupil simply divide the diameter of the objective lens by the power of the lens.
Eye Relief is the maximum distance at which the spotting scope can be kept from the eye without obstructing the entire field of view. The longer this distance is the les strain it would cause your eyes while looking through it for long durations.
Field of View
The field of view refers to the entire hemispherical area that can be observed at once or in portions through the spotting scope. A wide view is suitable for fast moving objects whereas a narrower view is required at higher magnifications.
Objective Lens Size
The second number in the magnifying power of a spotting scope represents the size of the objective lens. The larger the size, the more light it allows to enter the spotting scope. As a result, the image is brighter and has greater contrast and clarity.
Most prisms in these optical devices are made from BK-7 or BAK-4 glass. These prisms and their constituents and arrangement determine the quality of image that you get. In a Roof prism system all the prisms lie in a single line just behind the objective lens producing a narrow streamlined effect. In a Porro prism system, the prisms lie a little displaced from the objective lens offering a greater field of view and more depth of perception.
The spotting scope like all optical devices requires a firm tripod to function properly. The stand should be steady and not stand as an obstacle to the clarity of the image. Moreover it is essential to invest in a good spotting scope as the cheaper versions do not offer anything worth spending money on.