Zeiss  8x50

The Porro prism design (below, left) is the most classical optical layout in binoculars. Although this design is hardly used in modern binoculars, it provides twice as much stereoscopic effect of the subject. The stereoscopic effect of binoculars is calculated as follows: The ratio of the distance between the objectives to the eye times the magnification. For this 8x50 binocular, it's 2 (the objective distance is twice as much as the distance between the eyes) times 8 (magnification), or 16. It means the stereoscopic effect is magnified eight times.

Optomechanical design of Zeiss 8x30 binoculars (since 1952) utilizing porro prisms for correcting right side up image orientation, and high improved image with their 5-element Erfle eyepieces.

In Porro design, each prism had to be mounted, and cemented in place on the main diecast housing. A fine alignment was performed at the final stage of assembly by rotating an excenteric ring around each objective lens. These excentric rings are placed around the objective lenses, and below the front retaining rings.