Leica 77, Brochure

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Glossary
Light transmission, the degree of same When light rays strike on glass
surface, only some of them penetrate the glass, the others are reflected. The
more light penetrates a lens element or an optical system, the higher is their
transmission. As a rule, there is an approximate 4 % light reflection at every
glass-/air surface of an uncoated lens. This effect increases exponentially the
more lens elements there are in an optical system (in Leica binoculars there
are up to 11 optical elements = 22 glass-/air surfaces).
Coatings In order to minimize the reflection of light rays, complex procedures
are employed, involving the vapor deposition in high vacuum of numerous
layers of exceedingly thin layers of approximately 0.000125 millimeters, which
corresponds to 1/500 of the thickness of a human hair. At Leica, high-perform-
ance broadband coatings are applied that are tailored specifically to the types
of glass that are being used. Not only do they have the task of elevating the
transmission of an optical system to a close as possible to 100 %, they also
have the important task whenever possible to protect the particularly exposed
external lens surfaces from environmental influences and from damages such
as scratches. These two requirements – high transmission and high environ-
mental- and scratch resistance – are combined in the innovative multi-layer
coating Leica HDC™.
Prism systems Prisms have the task of bringing in-
verted and laterally reversed images of an object back
into the right position (which is why they are also called
reversing systems). The prisms used in such systems
have a decisive influence on the construction and the
compactness of a binocular. There are two several types
of prism systems, such as roof (left) and porro (right).
Phase correction coating P40 The P40 layer on roof prisms has the task of increasing the sharpness of the image and reducing
disturbing reflections and stray light. Without a P40 coating on the prisms, light sources are rendered with radiating star effects.
With a P40 coating they are reproduced very naturally. In this regard and in direct comparison, the qualitative differences of
different optical brands become obvious very quickly.
100 % light
Lens without coating
Lens with Leica HDC™ multi layer coating
approx. 8 % reflection
(4 % glass-air surface) 92 % transmission
100 % light
approx. 0,3 % reflection
(0,15 % glass-air
surface) 99,7 % transmission