Archived posting to the Leica Users Group, 2001/11/15

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Subject: RE: [Leica] Responsiveness of M6 meter at f/1.4 to f/2
From: Peterson Arthur G NSSC <PetersonAG@NAVSEA.NAVY.MIL>
Date: Thu, 15 Nov 2001 10:25:56 -0500

John,

I don't know, maybe it's "normal," but it don't seem right.  1.4 is 1.4, or
should be.  Seems to me what you're saying is that the Summilux is really
only a 1.5 or 1.6 lens because of vignetting, and the Noctilux only a 1.1 or
1.2, no?  Unless the optical system somehow affects the meter differently
than it does the actual exposure on film.  What am I missing here?  I don't
pretend to know the answer; I'm just asking questions.

:-)

Arthur G. Peterson
Alexandria, Virginia


- -----Original Message-----
From:	John Collier [mailto:jbcollier@powersurfr.com]
Sent:	Thursday, November 15, 2001 9:50 AM
To:	leica-users@mejac.palo-alto.ca.us
Subject:	Re: [Leica] Responsiveness of M6 meter at f/1.4 to f/2

It is normal. The inherent vignetting of any optical system wide open causes
this effect. It is most noticeable with the Noctilux. See Osterloh's Leica M
book for a well illustrated explanation.

John Collier

PS: Try your local library for the book. I might be persuaded to scan the
relevant sections out of my copy if you cannot locate it.

> From: Ray Moth <ray_moth@yahoo.com>
> 
> I've just noticed a peculiarity in the behaviour of the light meter in
> my M6 TTL, using a 50mm Summilux-M lens. If I adjust the aperture from
> f/1.4 to f/2 or vice versa, the meter doesn't register any change,
> whereas a change in shutter speed does register.
> 
> For example, if the meter indicates that f/1.4 at 1/500 sec. will give
> the correct exposure, then I would expect f/2 at 1/250 sec. would give
> the same indication but it doesn't; it shows over-exposure, as if I'd
> selected the slower shutter speed but left the lens aperture at f/1.4.
> Conversely, if I started at f/2 and 1/250, a change to f/1.4 and 1/500
> would indicate an under-exposure. The lens aperture selector seems to
> function properly. Has anyone else experienced this problem?


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Replies: Reply from "Ted Grant" <tedgrant@home.com> (Re: [Leica] Responsiveness of M6 meter at f/1.4 to f/2)