[Leica] KINOPTIC lenses

[Frank Dernie <FrankDernie@compuserve.com>]

Jim Brick wrote

>Could be... But I suspect that it's the front element coating more than<
>anything. That is, BTW, the first line of defence against flare. And
since<
>the flare occurred with bright objects or stray light hitting the front<
>element, I'm convinced that it is a coating problem.<

Sorry Jim, you have IMHO got this COMPLETELY the wrong way round. There are
a number of parameters affecting flare, the most important being the
geometry of the lens (number, position and shape of elements). There are
vrious ways of reducing the flare caused by these design limitations. These
include baffles, antireflection coatings on internal surfaces and surface
coating of the lens elements. If we just consider the lens element coating
the LEAST important coat is that on the outer surface of the front element.
The most important are the coatings on closely spaced and/or highly curved
internal elements.

This is obvoius when one considers that the flare is caused by light
reflected around in the optical system adding to the direct image forming
rays. Light reflected off the front surface can only be reflected backfrom
the inside of the lens hood. However light reflected back due to
shortcomings in the coating of the inner surface of the front element, for
example, would then start a back and forth flare producing set of
reflections. This is potentially even worse with closely spaced and or
highly curved surfaces where a multitude of back and forth reflections of
oblique rays cause a large area of flare.

I could go into much more detail:)

The most important appect affecting the flare potential of the lens is the
mechanical and optical design. Coatings allow designers to "get away with"
design shortcomings which would have made a lens completely unuseable
otherwise, but is really a second order effect. It is possible the design a
lens to be theoretically sharper if the reality of intternal reflections
are ignored, but such a lens has strictly limited applications.

IMHO it is the superior control of the adverse potental effects of internal
reflections which is the dominant factor in the real life superiority many
people observe in Leica lenses.

Best regards
Frank