Canon 10 x 30 IS Technology Guide - Page 4

Q1 What Types of Binoculars Are There? The first binoculars were invented about 400 years ago. There are now several hundred different models of binoculars manufactured and sold throughout the world. Although the concept of seeing a magnified image with your own eyes has not changed, there are two distinctly different types of binoculars: prism binoculars and Galileo binoculars. • Prism Binoculars The majority of binoculars sold today use convex lenses for both the objective lens and eyepiece lens. They are called prism binoculars, because prisms are used to "correct" the inverted image. 1) Porro Prisms (Fig. 1) Because of the porro prisms, the light passing through forms a "Z" shape before reaching the eye. 2) Roof Prisms (Fig. 2) When using roof-shaped prisms, called Roof (or Dach: meaning roof in German) prisms, the light passes through in a straight line, which makes it possible to design compact binoculars. • Galileo Binoculars (Fig. 3) The concept used in the telescopes made by Galileo Galilei in the 17th Century is used in these binoculars. Because concave lenses are used for the eyepiece lenses, prisms are not needed to correct the images. Also known as opera glasses, this type is used for looking at objects not too far away. 4 Eyepiece lens Porro prisms (Fig. 1) Objective lens Eyepiece lens Roof prisms (Fig. 2) Objective lens Eyepiece lens (Fig. 3) Objective lens