Binoculars are indispensable tools for watching wildlife and these days there are countless brands and features available to consumers. Yet despite the many options available, all binoculars use one of just a few different prism types, the most common of which are: roof prism, porro prism, or reverse porro prism.

To tell what kind of prisms your binoculars you have, it's best to look in the specifications for your binoculars (you can find these either on the manufacturer's website or in the documents that came with your binoculars).

Alternatively, you can often tell what prisms your binoculars use by looking at the arrangement of its lenses. Binoculars have two sets of lenses: the eyepieces (the lenses that you hold up to your eyes) and the objective lenses (the lenses that are farthest from your face when you look through them).

If the eyepieces are in line with the objective lenses (your binoculars are shaped like the letter H) then you probably have a roof prism design (top photo). Roof prism binoculars are a fairly new design that have a straight profile with eyepieces in line with objective lenses.

If the objective lenses are much wider apart than the eyepieces (your binoculars are shaped a bit like the letter W) then you most likely have a porro prism design (middle photo). A porro prism is the classic design, with eyepieces set closer together than the objective lenses.

If the eyepieces are set further apart than the objective lenses, then you have a reverse porro prism design. This is a common design for compact binoculars.

Which type of prisms are used in your binoculars?

• Roof prism
• Porro prism
• Reverse porro prism
• Other

View results →

Photos courtesy Nikon.