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Re: [OM] 40/2, focusing screens and OM1 pre-MD, was: various

Subject: Re: [OM] 40/2, focusing screens and OM1 pre-MD, was: various
From: "Carlos J. Santisteban" <zuiko21@xxxxxxxxx>
Date: Wed, 3 Mar 2010 14:22:11 +0100
Hi Edward and all,

From: "Sawyer, Edward" <Ed.Sawyer@xxxxxxx>

>> The 40/2 is also a lens that freely expands AND
>>happens to be a symmetrical design.
>
>Actually, it's not even close to being symmetrical. It's a typical gauss
design, >the unique thing being no cemented elements. (6 elements, 6
groups).

Well, a typical doble-gauss is, by definition, an almost-symmetrical
design...

The only reason for a fully-symmetrical one (like the Zuiko 80/4 Macro) is
to have a fully symmetrical system, where the projected images matches the
original subject in position and SIZE -- thus the 1:1 macro ratio. The
advantage of such layout is that most aberrations get cancelled, but only
for 1:1 reproduction.

That said... I don't think the 40/2 is a really typical doble-gauss... I
think what defines such design is to have a couple of opposite doublets
(cemented or not) with their negative components facing inwards, and the
positive outwards. Depending on speed, some additional correcting elements
(mainly positive) may be added at either side, usually stronger at the image
side, because of the asymmetry of depicting distant objects. These
correcting elements are usually around the Gauss-doublets -- the enlarging
Schneider Componon-S (only on the inside) and CV's Nokton 35/1.4 (two inside
and two outside) & 40/1.4 (one inside at the back, two outside) being
notable exceptions.

Well, in the Zuiko 40/2's front doublet (separated), the positive element is
facing the film, and the negative element faces the subject -- just the
opposite os the usual layout. Maybe it makes it a tiny bit on the retrofocus
side, since its focal length is actually shorter than the OM mount's
register (46mm)

>Re: the 38/macro and screens:  the 1-11 and 1-12 will be best for this
lens. I
>had both at one point, I liked the 1-12 the best. The varimagni is a must,

Indeed. As you said, it's however very nice for the angled view. The 1-12 is
a weird thing, but it seems to be great for extreme macro, as intended.

BTW, I got recently from "that auction site" a black OM-1 with data back 3.
Supposedly, the light meter wasn't working... Upon arrival, there were
several "surprises":

-It's a pre-MD unit (20xxxx)
-Cosmetically very nice, however the slight brassing doesn't show any brass,
but chrome... maybe it was a chrome model repainted black?
-Some pentaprism desilvering at the bottom -- just like my other Pre-MD :-(
-There was an A625 battery on it... installed backwards! The meter is indeed
alive and, at first glance, looks accurate.
-Shutter checks out OK -- tested with a TV, no capping even at 1/1000, slow
speeds not sticky at all.
-Somewhat coarser than my old chrome pre-MD, could use new seals anyway --
easily solved.
-Without the external cable, the data back 3 won't work on it -- needs
1n/2n/2S or the 3/4 series. Otherwise seems to work fine on the 2n (as soon
as I develop the test roll, I'll know for sure)
-It had a 1-12 screen on it!

However, the problem with these pre-MD units is that they won't accept a
regular OM back, they need a special one with narrower pressure plate...
otherwise the film won't stay flat, and will get an accidental tilt -- been
there, done that. On the other hand, the data back 3 seems to have a couple
of holes on its pressure plate that allow it to be used with the pre-MD
units...

Is there a chance nowadays to get a short-plate back for it? Or is it safe
to remove the two "offending" screws on the body???

Thanks a lot in advance,
-- 
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
-- 
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