Roof Prism Design

Roof prisms in binoculars.

Roof prism design.

Today roof prisms dominate the top end birding binocular market. The design of the prisms means they work together to correct blurred images and let you see your target clearly. These two 90 faces resemble the roof of a building giving this prism type its name. There are two prisms and these meet at a 90 angle with the shape looking similar to the roof of a house.

Differences in binoculars build and design. Built to last in a harsh environment a roof prism binoculars central portion that connects the 2 tubes is either an open bridge or closed bridge design. A roof prism also called a dach prism or dachkanten prism from the german. Dachkante lit roof edge is a reflective optical prism containing a section where two faces meet at a 90 angle.

Reflection from the two 90 faces returns an image that is flipped laterally across the axis where the faces meet. The open bridge design has a focus mechanism close to the eyepiece with the stabilizing section towards the objectives while the closed bridge design has an enclosed focus mechanism. Roof prisms are the newer option. Roof prisms enable slim binoculars.

Nevertheless the roof prism design s appeal was so great that manufacturers went all out to perfect it. While light loss and transmission rates are huge factors in optical quality there are many other factors that allows a roof prism bino for possible. The porro prism design was simpler and more light efficient and its images showed better contrast.