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Re: [OM] Focusing Screens

Subject: Re: [OM] Focusing Screens
From: GPaul64@xxxxxxx
Date: Fri, 30 May 2003 17:10:54 EDT
In a message dated 5/30/2003 4:41:07 PM Eastern Daylight Time, piers@xxxxxxxx 
writes:


> I'm still not sure I'm with you Dan.  Past infinity?  Surely not - we'll
> have someone chiming in with Buzz Lightyear comments if we ain't careful!
> 
> Perhaps what you are seeing is the ability to bring the lens into focus on
> something in the distance, and then go out of focus again - but that would
> be because "in the distance" actually isn't at infinity.  That's a
> phenomenon I experienced when first using a 500mm mirror lens - it's as if
> infinity has syuddenly jumped back a mile or ten.  But not a 'fault' with
> either lens or camera.
> 
> Piers

Lenses focusing "past infinity" are actually common.  For example, the 
focusing ring on the venerable Zuiko 300mm 4.5 can be rotated past the infinity 
mark.  This allows the lens to focus accurately to infinity at very cold 
temperatures, when the metal lens barrel may have contracted.  Accordingly, at 
normal 
temperatures, the lens does indeed focus a little "past" infinity.  

Interestingly, though, the guy I bought my 300 zuiko from was named Buzz.... 
;-)

Best,

Greg L. 

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