Optical Systems and Binocular Size

Light enters the objective lenses and travels via prisms to the eyepieces.  The two most commonly used prism systems are:

• Porro prism (named after Ignatio Porro,the Italian physicist who invented them in 1823 and first used them in binoculars), and

• Roof prism.

These two types of systems have resulted in two basic design types:

The Classic design.  A distinctive “Z” shape characterised internally by the use of a combination of two right angle porro prisms and externally by the offset positioning of the eyepieces from the objective lenses.

Roof prism design. With the prisms positioned one over the other, the objective lenses and the eyepieces are in line. The result is a more compact design which allows compact binoculars to have full size power capabilities.

This is not to say that all of Tasco's compact binoculars utilise a roof prism design although most do, nor that all of our larger binoculars utilise a Porro prism design although most do - (a notable exception are the superb Tasco Titan binoculars).