Roof prism binoculars are straighter and more streamlined. Porro prism binoculars tend to be larger and have a definite offset to their body design. Porro and roof prism binoculars are distinguished by their shape. There are generally two categories of prisms, porro prisms and roof prisms. However, lens coatings, lens alignment, quality of glass, and quality of prisms also affect how sharp a viewed image will be.

The larger the diameter of the objective lens, the better the resolution.

Resolution is primarily determined by the objective lens diameter. Wider field of views are often preferred by hunters who want to scan large areas for game or for viewing sporting events.ĭescribes how sharp or clear an object appears when viewed. An example field of view for a standard 7X binocular would be 372 feet, whereas a wide angle would be 487 feet. On wide angle binoculars (designated WA on Alpen binoculars) a special lens design allows a wider field of view than normal. Expressed as the number of feet per 1000 yards of distance, the higher the magnification the narrower the field of view. Binoculars with 'long eye relief' provide from 14-20 mm (or more) eye relief.ĭescribes the size of the area that can be seen through the binocular or spotting scope. Most binoculars provide 8-13 mm of eye relief. Binoculars designed with long eye relief are usually preferred by those who wear eyeglasses. Eye relief is affected by magnification, the number of lens elements, and field of view. A 10x50 binocular magnifies objects 10 times and has an objective lens diameter of 50 mm.Įye Relief is the distance, expressed in millimeters, from the ocular (eyepiece) lens to the point where the eye is positioned to view the entire image. For example, 7x35 means the binocular magnifies objects 7 times and the objective lens is 35 mm in diameter. The first number is the magnification and the second number is the diameter of the objective lens in millimeters (mm).

Binoculars are normally identified by two numbers.

Binocular prism alignment