What Do the Numbers on a Spotting Scope Mean?
Spotting scopes can be valuable tools for watching land based objects at a distance. Spotting scopes are basically scaled down telescopes that can be carried. Understanding what the scope's numbers mean can be vital when choosing the right scope for you.
Magnification Defined
Magnification is the optical illusion (produced by lenses) that an object is closer to you than it really is. Magnification power refers to how large the object appears as compared to unaided eyesight. For instance, if a scope is listed as 2x, then objects will appear twice as large when viewed through the scope.
The Scopes Magnifying Power
The first two numbers of a spotting scope description state the scope's magnification power (the "X" following the numbers signifies magnification power). If a scope is listed as a 15-50x 80mm scope, that indicates that the scope's lowest magnification setting is 15 times that of normal vision, and the highest magnification setting is 50 times greater.
The Objective Lens
The last number on a scope description is the size of the objective lens in millimeters. The function of the objective lens is to channel light into the body of the scope. The clarity of the scope's picture is directly proportional to the amount of light brought in. A large objective lens is particularly desirable for viewing objects at a great distance.
The Field of View
Although not listed in the spotting scope description, the field of view is still an important number. The field of view (FOV) is a horizontal measurement of the viewable area as seen through the scope. For example, a scope may have an FOV of 91 feet across when set at 20x and 45 feet across at 60x. As a rule, the FOV decreases as the magnification increases.
The Clear Focus Distance
The clear focus distance is the minimum distance that an object must be from the scope to be seen in focus. For example, if a spotting scope has a clear focus distance of 23 feet, then an object must be at least 23 feet away to remain in focus. A low clear focus distance is particularly helpful for nature watching.
Tags: scope description, spotting scope, clear focus, clear focus distance, feet across, field view
