[Leica]lenses & dust

[Erwin Puts <imxputs@knoware.nl>]

>I think that Erwin has run tests on lenses that were new off the shelf and
>older ones but I wonder how clean the older lenses were. -- Marvin Moss

I do tests with new and older lenses. Some are indeed off the shelf, but
most are not. Whenever possible I use my own lenses (usd but from recent
production runs). Most older lenses are not clean. You would be surprised
how much dust you can see in a lens when a strong light source is beaming
through the glass.
Technically I am not all concerned about or interested in dust, even
relatively large amounts of it. The optical performance is hardly affected
by dust. When comparing clean lenses and lenses with a fair amount of dust
between the glass elements I failed to notice any degradation.
Personally I would venture to suggest that dust between lens elements is
purely cosmetic. You may feel annoyed and disturbed by its presence, but
performance- wise it is innocent.
Maybe the collector and the user should switch their set of criteria. I
must confess that I hardly ever look into my lenses searching for dust.
Scratches and fingerprints on the surface are my concern, not dust or air
bubbles or even little pieces of paint.
You may feel entitled to impeccable cleanliness from Leica lenses and blame
QC if a lens does not live up to expectations (giving the amount of money
paid for it). I am paying for optical performance and durability and yes
some esthetical pleasure. But maybe I know too much about Leica lenses and
are becoming a bit tolerant on all aspects that do not influence
performance.

Erwin