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Re: [OM] Zuiko 28mm/f2.0: Shades & Coatings

Subject: Re: [OM] Zuiko 28mm/f2.0: Shades & Coatings
From: "John A. Lind" <jlind@xxxxxxxxxxx>
Date: Mon, 12 Jun 2000 22:27:11 +0000
At 18:19 6/12/00 , Giles wrote:
>
>I just knew when I wrote it I was going to be corrected ;-)
>
>Giles

Sorry Giles,
It wasn't intended as a "correction" and better wording on my part would
have said "a *good* ballpark approximation," especially for the Zuiko's
which were designed to be compact and light weight.

It was intended to provide simplified mathematics from which your
approximation was derived, better understanding about lens apertures, and
give some insight about front element diameter as it relates to lens speed
and focal length.  Your logic behind your approximation is good.

Someone mentioned the possibility the "floating element" has some
correlation to the ring size.  Hans' Sales Information File page on the
28/2 mentions its floating element for close focus correction.  A check of
Paul Farrar's page with Zuiko lens data has some interesting notes about
the 28/2.
 ( http://www.datasync.com/~farrar/zuiko.html )
His two notes mention the possiblity of 3 versions of the lens, the
earliest of which may not have had the floating element.  It has always had
a 49mm ring though.  The 24/2 has a floating element, but the 35/2 does
not.  All three date back to at least January 1974 for the OM system
(earliest date shown in the SC versus MC table on Lee Hawkins' web site).

Perhaps the difference is based on who the lens designer was and/or the
basis from which the design was derived.  Many lenses are derivations of
earlier designs, some dating to the beginning of the 20th Century.  I'm
wondering if the 28/2 is a symmetric design, and the 24/2 and 35/2 are
asymmetric designs (or vice versa).  Just stabbing in the dark about
another possible correlation.

Olympus provides (or at least provided) a data sheet containing DOF tables
and a cutaway view of the lens (without dimensions) in the box with each
lens.  I think most of these get chucked into the trash along with most of
the other papers.  It would be interesting to compare cutaway views showing
the element and group configurations on the three lenses.  It is sad this
information was not provided in the OM Sales Information Files (or was it?).

-- John

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