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[OM] Re: OM lenses

Subject: [OM] Re: OM lenses
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Thu, 08 Nov 2007 21:01:05 -0500
You need to differentiate strongly between Olympus OM mount film cameras 
(manual focus, mostly mechanical and first released in 1973) and the 
more modern Olympus 4/3 mount digital cameras announced starting with 
the E-1 in 2003... some 30 years later.

Only independent lens makers such as Tamron, Tokina, Vivitar, Soligor 
and a host of others made OM mount lenses besides Olympus.  The Olympus 
OM mount was considered proprietary and no other manufacturers ever made 
OM mount camera bodies.  The 4/3 mount, on the other hand, is considered 
an "open" standard.  Not free but you can get the specs and build your 
own if you like.  Leica and Panasonic also build 4/3 mount cameras and 
lenses and since the 4/3 mount is a standard their 4/3 mount lenses will 
also fit Olympus 4/3 bodies and vice-versa.

All camera mounts have what's called a "registration distance".  This is 
the distance where the lens comes to infinity focus behind the base of 
the lens flange or the distance from the camera's lens flange to the 
surface of the film or sensor.  In the case of 4/3 bodies this distance 
is rather short compared to an OM body or 1/2 dozen other contemporary 
film camera bodies such as Nikon.  Since the OM registration distance is 
longer than the 4/3 body it's possible to build a mechanical adapter to 
join the disparate bayonet mounts while still having enough room to 
spare that the OM lens can still reach infinity focus on the 4/3 body. 
The same goes for Nikon mount lenses and some others.

But this most definitely does not work in reverse.  You can't put a 4/3 
lens on an OM body since its registration distance is not long enough 
for the lens to focus on the film at infinity.  And even if you could 
the lens isn't designed to provide an image circle large enough to cover 
35mm film.

Chuck Norcutt


Matthew Granger wrote:
> So the correct term for the OM style mount is bayonet mount M-1?
> 
> Also, I heard that other brands (maybe Leica?) make lenses that fit onto OM
> or Olympus digital. Can anyone tell me where to get info on this?
> 
> matt

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