PD is the distance between the exit pupil and the last lens vertex of the eyepiece(s).
Phase correction (P-Coating) (P)
In binoculars with roof prisms (Abbe-König and Schmidt-Pechan), interference results in an unfavourable intensity distribution impairing resolution. This becomes particularly apparent at high magnifications and small exit pupils. The deposition of dielectrical layers on the roof surfaces (P coating) corrects this effect in such a way that the contrast and resolution provided by Carl Zeiss roof prism binoculars are markedly increased. All Zeiss binoculars containing roof prisms are provided with this phase correction coating which significantly improves resolution.
Four types of reversal prism are used which determine the design of Zeiss binoculars
The generic term used to describe Pechan and Abbe-Koenig prisms is roof prisms.
- Porro 1: Wide-bodied binoculars with a low height, e.g. 7x50B/GA
- Porro 2: Used in the monocular and binocular 20x60S
- Schmidt-Pechan: compact binoculars, e.g. all pocket binoculars from Carl Zeiss
- Abbe-Koenig: Long, slim binoculars, e.g. Victory 8 x 56 B T*