A primer for binoculars

There are countless criteria that concern the performance capability and suitability of a binocular or spotting scope. We have selected and briefly described the most important concepts and characteristics for you.

Magnification: Magnification is a measure of how much closer an object appears to the viewer. At an 8x magnification, an object situated at a distance of 100 m [328 feet] appears to be as large as if it were only 12.5 m [41 feet] away (100 : 8 = 12.5); [328 : 8 = 41]. Binoculars are identified with two specifying numbers, like 10 x 42, for example. The first number indicates the magnification factor.
Front lens diameter: This is the second number in the specification of a binocular or spotting scope. A 10 x 50 binocular has a front lens diameter of 50 mm. The larger that number, the more light can be gathered by the binocular. 42 or 50 mm for instance, are suitable for observation in twilight, whereas 20 mm is suited for viewing in daylight.
Exit pupil: The exit pupil is the bright circle that can be seen when looking into the eyepiece of a binocular from a distance of approximately 30 cm (12 inches). The larger the exit pupil (exit pupil = front lens diameter in mm divided by the magnification factor), the brighter the image in twilight. It should be noted that an exit pupil with a diameter greater than 6 mm usually cannot be fully utilized by viewers who are more than 30 years old.
Twilight factor: This number describes the performance capability of a binocular in twilight. It is computed by taking the square root of the product of the magnification factor and the front lens diameter. The twilight factor can, however, only serve as an approximate guide, because it does not take into account the quality of the optics.
Objective field of view: This value indicates the width of the field of view at a distance of 1000 m (approximately - of a mile). In general, the higher the magnification, the smaller the field of view. Here too, Leica binoculars show their superior strengths.
Internal focusing: With Leica internal focusing, the only part that is shifted is a lens in the interior of the binocular or spotting scope. Because nothing is shifted on exterior surfaces, neither air nor humidity are drawn in - a clear view is uniformly preserved, even in murky weather.
Eyepieces for eyeglass wearers: When a binocular is to be used by someone who does not wear eyeglasses, the sliding eyecups should be pulled out. For eyeglass wearers, the sliding eyecups are simply pushed in. This allows the eyes always to be positioned at the same distance to the eyepiece, so that they can always see the full field of view. This is made possible by Leica eyepieces especially designed with exit pupils positioned at the right distance away from the eyepiece.
Multi-function central operation: Central operation permits simultaneous focusing of both halves of the binocular. Furthermore the combination wheel patented by Leica allows convenient diopter compensation for both eyes, independently of one another. Once the diopter compensations have been set, their values can be read on a scale and they can be reset quickly when the binocular is used again at another time.
HDC™ optical coating: The lenses in all LEICA TRINOVID BN and compact binoculars are treated with HDC™ optical coating (Highly Durable Coating). This innovative multiple coating is more scratch-resistant than conventional multiple coatings - a major advantage, especially for external lens surfaces

This page was last updated: 01/28/2004 20:42:46 -0500

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