Chris, I'm afraid I've stepped into the advice trap. Trying to describe how
to inspect a lens for coatings and, especially, flaws, is best done with
illustrations or, better yet, the personal touch.
Coatings can be seen by tilting the lens slightly away and checking the
colors of the light fixture reflected in the glass. For example, with my
75-150/4 I see a single large magenta-tinted reflection of the light fixture
I'm using and several smaller yellowish reflections. All are distinct,
sharp and even.
Mottling from separation, on the other hand, would appear as oil on a
puddle. Or two sheets of glass with a thin smear of oil between them. To
see it you'd have to look directly through the lens, rotating it slowly and
tipping it very slightly as you go. Fungus or mildew *might* cause a
similar appearance, but not likely.
To get an idea of what fungus typically looks like, check this URL:
http://www.chem.helsinki.fi/~toomas/photo/fungus/
To get a better idea what good, clean glass, single- and multi-coated,
should look like, check Tom Scales' site. In many of his lens photos you
can see straight through them - excellent work:
http://www.zuikoholic.com/Zuiko.htm#Zuiko Prime
Hope this doesn't confuse matters further.
Lex
===
From: "Chris O'Neill" <coneill@xxxxxxxxxxx>
Subject: Re: [OM] THE GRAIL! (Wuz "Vivitar 285 flash for Oly 75-150mm
lens...)
Date: Sun, 30 Jul 2000 11:46:44 -0600
He had several (3 or 4) sitting on the shelf. The one I looked at had a
sticker saying CDN$195 on it ('bout US$130), but nobody ever goes by
that. My guess is that I could have slapped down around CDN$125 ('bout
US$85) and walked out with it.
Of course, it was *not* multi-coated. My mistake. I tooked at the
reflections in the front element and saw a bit of a rainbow, so I assumed
it was multi-coated. (That *is* how you tell, isn't it?) I think you were
suggesting that this might indicate that the elements are separating,
right???
Chris
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