Ted's Cameras Learning Centre

Binocular Buying Guide

8 August 2017 11:39:53 AM AEST

Binocular types, features and sizes vary greatly based on their purpose, ranging from small, foldable binoculars for the theatre or opera, to high-powered, tripod-mounted binoculars ideal for those interested in astronomy. We explain some basics around different types of binoculars and their common features, and give some tips on what to consider when buying binoculars.

How do binoculars work?

Binoculars incorporate at least two lenses: the objective lens (or distal objective lens assembly), which is closest to the object, and the eyepiece lens (or ocular lens assembly), which is closest to the human eye. Generally combining convex and concave lenses, the objective lens forms a clear image that is magnified by the eyepiece lens.

The most common kind of binoculars are prism binoculars. Using convex lenses for both objective and eyepiece lens, a prism system is incorporated in the optical path to rectify the inverted image projected by the objective lens. The use of a prism system in binoculars as illustrated below allows for a much more compact body compared to the Galilean binoculars that don't incorporate prisms.

porro, roof galilean binoculars

Binocular Types

Porro prism binoculars:
In general, there are two types of prism binoculars: porro prism binoculars and roof prism binoculars. The optical path in porro prism binoculars is bent like the letter Z, which means the image formed by the objective lens is reflected by two prisms. The design of this prism system gives the binocular its distinctive offset shape: the eyepiece lens and objective lens are not aligned. Due to the completely reflective surfaces in the prism assembly, no light is lost on its way from the objective lens to the ocular lens assembly. Porro prism binoculars are easy to produce, which may be a reason why they are more commonly used than the more expensive roof prism binoculars.


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