Re: [Leica] lens repolishing

[Alfred Breull <puma@hannover.sgh-net.de>]

Does anybody know an answer on Anras' question ?

Alf
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At 08:07 24.01.1998 -0400, Andras Iklody-Szabo wrote:
>On various occasions there were mentions on this list of scratched lenses
>which could be restored to as new condition, but this was not considered an
>economically feasible solution.
>
>Let's forget about the cost for a moment! What I do not understand with
>this procedure is, how can a lens be restored to as new condition
>photographically (not cosmetically), when repolishing alters the lens'
>geometry. Factory tolerances when grinding lenses are in the order of
>.001mm or so. A scratch on the front or back surface of a used lens can
>easily be of the same order of magnitude, if not more. To grind (polish) it
>away, you have to take away that much glass from the whole lens surface
>(not just locally). That means that the geometry (thickness) of the lens
>and thus the path of the light rays through it are altered. Since the
>damaged lens surface is usually up front, this alteration changes (if ever
>so slightly) the path of the light rays through the folloing lenses in a
>multielement lens as well.
>
>How does all this affect photographic quality? Does it only translate into
>a slight shift of focus for which the lens is then adjusted (e.g. the
>polished element shimmed) or is there more to it? I am not an optical
>expert but somebody on the list might be. Can he help?
>
>
>Andras Iklody-Szabo
>Caracas / Venezuela
>
>
>