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[OM] Re: Figuring out depth of field with 4/3 adaptor

Subject: [OM] Re: Figuring out depth of field with 4/3 adaptor
From: "Piers Hemy" <piers@xxxxxxxx>
Date: Thu, 31 Mar 2005 16:20:22 +0100
I was wrong on two counts.
The source I used for the 4/3 lens register says thus:
"The Four Thirds value computed as a difference between the OM one and the
thickness of the OM->4/3 adapter"  
And the OM register is 46mm, not 46.5mm
So in fact we know the thickness of the MA-1 (46 - 38.67 = 7.33mm), but we
don't know (yet) the 4/3 lens register. 

I don't have any better answer to Moose's posed conundrum.

--
Piers 
 
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Moose
Sent: 31 March 2005 11:19
To: olympus@xxxxxxxxxx
Subject: [OM] Re: Figuring out depth of field with 4/3 adaptor

Piers Hemy wrote:

>It must be because on a 4/3 mount, an OM lens is at a different 
>distance from the "film plane" than it was designed for.
>
>The register on an OM camera is 46.5mm, while the register on a 4/3 
>camera is about 38.7mm
>
>How thick is the MA-1 adaptor? 
>
Wayne Shumacher said back in July:
---------------------------------------------------------------
"The OM FOURTHIRDS Adapter given away by Olympus is as good as an OM auto
extension tube as far as quality of materials. The only thing I have noticed
is that infinity focus is just slightly off, that is you can over-focus,
which I assume means the thickness of the adapter is just slightly short.
I'm sure there is a good reason for that?"
---------------------------------------------------------------
And I may recall someone (? C.H?) else saying the MA-1 may be about 0.5mm
shorter than the Kindai.

The only straightforward reason I can see it to be sure that there is no
normal mount lens that cannot focus to infinity under any circumstances. 
Since all normal lenses focus to infinity on OM bodies, that doesn't make
sense. Any other, non-conspiracy, theories?

Moose


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