Sunday, January 29, 2012

All About Roof Prism Binoculars

Binoculars use prisms that redirect incoming light in different directions allowing it to travel a long distance in a small amount of space. A long focal length can be used in this way. Without prisms, the sides of binoculars would be as long as telescopes.

Most binoculars use either a porro prism design or a roof mounted design.

Porro prism binoculars use prisms that are offset at a distance from each other giving them their familiar dog-leg appearance. This usually makes them bulky and heavy.

Roof prism binoculars have prisms that are mounted close to each other at a 90 degree angle from each other. This avoids the offset design of porro prism binoculars. Unlike porro prism binoculars, the eyepiece is directly in line with the front objective lens.

This gives them a sleek look and makes them smaller and lighter-weight because large offset barells are not needed. For most people, they are easier to handle and focus..

They are also usually more rugged. With porro prisms the eyepieces moves in and out. In roof prisms the eyepieces do not move.

The objective lenses move within the barrels of the body where they are better supported and protected. When you focus them you will not see any outside movement of the lenses. Also, porro prism binoculars use rubber gaskets to seal the lenses. With the external movement, they eventually wear allowing moisture to enter the binoculars.

Typically, roof prism binoculars have been more expensive because more labor was used to make them. With updated construction methods however, the price of production has greatly been reduced. Now roof prisms with excellent quality can be had for reasonable prices.


  1. Very nice. Got knowledge about uses of Prism in binoculars. This is one of very informative post. Also I've shared this with my friends. :)
    Swarovski Binocular

  2. Thanks for your comment. Nice blog - I'm signing up via Google reader. Good birdibg

  3. This is good info..I bought myself a pair of decent bins from Eagle Optics last year.. ones with good eye relief...Michelle