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Re: [OM] True, or just BS?

Subject: Re: [OM] True, or just BS?
From: Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxxxx>
Date: Sun, 6 Jul 2003 17:56:22 +0100
In article , Albert <olympus@xxxxxxxxxxx> writes
There's a guy at my local photo club; a walking encyclopedia of
knowledge when it comes to lenses; because he's owned practically every
single one before.

One of the arguements we got into is coating.  He says Sigma's and
Tokina's have coatings that are prone to going bye bye within 3 years.
As I've never owned my lenses for that long (and my UV in front keeps
me from wiping my front element) I was wondering if this can be verified
by the list or not..

He said that sigma, tokina, canon, generally have coatings that are more
prone to being worn out.  Said Leica coatings lasts the longest..

True, or BS?  Or just how well you maintain the lens?

Wrong question - it might be true, it might be BS but either way it is meaningless twaddle of no relevance to any photographer for a large number of reasons, some of which have been mentioned by others.

Coatings on normal photographic lenses should not be subjected to any mechanical wear, so there is no concept that they "wear out". However they can be attacked by contaminants in the environment - ozone, acid rain etc. Some early coatings were actually porous, permitting the contaminant to attack the bond to the glass, so the coating peeled or flaked off. But that problem was solved long before anyone went to multicoating lenses.

If your buddy has serious problems with the mechanical robustness of coatings to his cleaning technique then he should consider investing in lenses made from this stuff: http://www.activglass.com ;-)

There are coatings which have been developed specifically for their hardness and ability to withstand abrasion, such as boron phosphide or diamond which are actually many times harder than the underlying glass, but these are not generally used in the photographic industry because the optical performance is inferior. They are used for systems which will encounter serious abrasion problems, such as missile optics, submarine periscopes and military aircraft cockpit windows and forward looking optical systems. Even on these systems, it is generally only the front surface which is hard coated - other surfaces use higher optical grade coatings.

I know the guy who invented the diamond coating system (and lent him my spare OM-4 - the one that developed a fault recently - for a couple of weeks about 20 years ago when his C@non broke on a visit to California). He occasionally tells the tale of how he wanted to find an alternative mass market application for his coating so that production costs could be reduced. Since diamond is a non-reactive material he thought that the coating might make a better non-stick surface for cooking than the Teflon that had become popular at the time. So he had his workshop treat and diamond coat a frying pan for him to try. The surface looked like a normal new copper bottom pan, bright and shiny, but it could be scoured with steel wool and wouldn't scratch at all. The problem appeared the first time he used it to fry an egg - it stuck fast to the bottom of the pan and no amount of scrubbing and scouring would remove it! I think he still has his diamond coated frying pan, complete with surface trace of egg, though it doesn't hang on his office wall any longer.

Try asking your coating expert to fry an egg on his lenses and prove the coating sticks better on Leicas than any other! :-)
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers

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