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Re: [OM] Lens Element Wear

Subject: Re: [OM] Lens Element Wear
From: ALEXSCIFI@xxxxxxx
Date: Sat, 29 Jan 2000 14:04:35 EST
Brilliant Ken--this is one of the finest technical dissertations of all time!

Alex

;o)

image66@xxxxxxx writes:

<< Questions come up periodically regarding why pros still use Leica
 rangefinder cameras.  The original reason has almost been forgotten--Lens
 Element Wear.
 
 Years ago when SLR cameras started to make a major headway into usage with
 the Nikon F bearing down on the photojournalism world it was quite apparent
 that the Leica lenses remained sharper than the Nikon's.  Opinions were
 formed by wannabe technoids, but conclusive research was done at the
 Fareway Lie Archival Research Enterprise (FLARE) and Golf Course.
 
 This research resulted in a startling discovery.  Photons flowing through a
 glass surface causes a molecular transfer throughout the lens element which
 can alter the overall shape and optical characteristics of that element.  As
 a lens ages, its optical formulation can actually change resulting in less
 resolving power.  Furthermore coatings can change and multicoated lenses
 will slowly fade into single-coated lenses.  All lenses were multicoated,
 but most of the older ones just have the yellow coating left.
 
 With rangefinder cameras such as the Leica, Photon flow is limited to only
 the times of the exposure, whereas an SLR will allow photon flow anytime the
 lenscap is off.  What is surprising is that 40 year old Leitz lenses
 exhibit less lens element wear than most SLR lenses subjected to just a
 couple hours of use.  Since the Leica rangefinder lenses don't wear out at
 nearly the same pace as SLR lenses they remain sharper longer.  Leica
 provided test lenses which were sealed against light contamination to the
 various photography magazines which is why Leica lenses always tested as
 among the sharpest in existence.
 
 Additional research revealed the cause of flare.  Lens elements can pass on
 only so many photons.  Excessive photons are stored in the lens element
 like static on a boy shuffling across a cheap carpet.  These stored photons
 manifest themselves as "flare".  Older lenses (mistakenly called single
 coated lenses) have more photons stored up which makes them more susceptible
 to flare.  Newer lens designs contain elements labeled ED, Rare-earth, ELD,
 etc. which do not store photons. These elements are also less susceptible to
 formulation alteration from usage too, but can suffer from
 DeUglyFaceCrackDeLens Syndrome.  It is important not to use these modern
 lenses around truely scary looking people.
 
 The rate of wear is expressed with the following formula:  YA=R(i)/GH-t
 The photon buildup is expressed as:  Ge=Tr-E/a+L
 
 To discharge the excessive photons from your older lenses the repair
 procedure requires you to place the lenses on their sides with the lens
 caps off.  A blacklight is placed in front of the lenses and an infrared
 lamp placed behind.  This must be done in total darkness, so it is best to
 use your darkroom for this procedure.
 
 Returning your lenses to multicoat status is not possible, but the effects
 of coat reduction can be helped by this procedure.  As always YMMV.
 
 Ken Norton
 
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