Archived posting to the Leica Users Group, 2002/07/08

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Subject: [Leica] 12 or 16 mm white spot on M
From: Christer Almqvist <chris@almqvist.net>
Date: Mon, 8 Jul 2002 17:20:57 +0200

The discussion about the pros and cons of the M7 has been quite 
educational for me. I was surprised to read that the white spot on 
the shutter curtain has a 12 mm diameter as I had always thought it 
was 16 mm. Where did I get my 16 mm from, I asked myself? Well wasn't 
there something about the size of the white spot in the manual? Yes 
indeed. My manual, printed 1994, says that the diameter of the white 
spot is two-thirds of the short side of the viewfinder frame for the 
lens used and that the white spot corresponds to 23% of the picture 
area. They arithmetics are certainly correct, two thirds of 24 mm is 
16mm which makes the radius 8 mm and therefore the white spot area 
200 sqmm which is 23% of (24 x 36 mm =) 864 sqmm.

So I looked at the white spot. It does not look like 16 mm. So I cut 
a piece of paper 16 mm wide and put it next to the white spot. The 
spot is certainly not 16 mm, it is much smaller. So I recut the paper 
to 12 mm, and yes, the spot is 12 mm. Seems you can't trust anybody 
these days, not even the Leica manual.

Knowing that the diameter of the spot is about half the length of the 
short side of the negative rather than two-thirds, will change my 
shooting habits. Much less moving up to measure the light off a 
person's face when shooting portraits, much less turning the camera 
down when photographing landscapes in order to avoid the effect of 
the sky when measuring the light of the landscape and so on.

On the same subject (you can't trust anybody these days), the usually 
reliable Réponse Photo in its July issue says that Leica M6 and M7 
measure the light of an area that corresponds to 13% of the frame, 
and, here it comes: with a 21 mm lens this makes it almost a spot 
meter, compared to using a 90 mm lens where it is much less 
selective. I think the author believes the area measured is 13% of 
the viewfinder frame, not the negative frame.   I see this exactly 
the other way round. If you need a spot meter when taking pictures 
with your 21 mm lens, but you have none, then put on a 90 mm or 135 
mm lens as that will help you measure a small area more exactly than 
with a 21 mm lens (provided you measure form the same standpoint). 
The problem with this is that by the time you have put the 21 mm back 
on the cameara, the light has changed anyway.

One other thing that surprised me reading the M7 experience of some 
of the more eloquent contributors, is how pleased they were with 
having so many perfectly exposed negatives. Exposure problems are 
much less of a problem for me than perfectly focused negatives

...and look at my webpage

Chris
- -- 
Christer Almqvist
D 20255 Hamburg and / or
F 50590 Regnéville sur Mer
http://www.almqvist.net/chris/new
- --
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Replies: Reply from Mark Rabiner <mark@markrabiner.com> (Re: [Leica] 12 or 16 mm white spot on M)
Reply from Ted Grant <tedgrant@shaw.ca> (Re: [Leica] 12 or 16 mm white spot on M)