Binocular prisms

24 October 2019

Ever wondered what’s inside your binoculars? Take it from me, there’s some complicated stuff in there.

The most important part of the binocular is the pair of prisms between the lenses. Without these, you’d be seeing upside-down.

Design and quality of prisms can make a great difference to the quality of the image you see through the binoculars.

They can also make a big difference to the look of the binoculars themselves. The older-style “porro” binoculars, with their characteristic zig-zag shape, have largely been displaced by “roof prism” binoculars, which have a straight-through look.

This may or may not be a good thing, as while roof prism binoculars are more compact, more robust and easier to waterproof, most of them don’t provide as bright an image as their predecessors.

Thanks to our friends at saxon, I got to pull a pair of binoculars apart and investigate the prisms inside them. I’ve written a blog about it (at, complete with photos and diagrams.

Sadly, I have to report that the patient did not survive the procedure. But thanks to their sacrifice, I can show you how they worked without your having to do your own “destructive investigation”.