Re: [Leica] 13% or 23% ?

[Christer Almqvist <chris@almqvist.net>]

This is confusing. But it is worthwhile to try to understand it. And 
you are not the only one to be confused. The penultimate issue of 
Réponses Photo said that the area measured expressed as a percentage 
of negative size got smaller and smaller as you change from wide 
angle to telephoto lenses. Absolute bs, and they corrected the error 
in the current issue.

First of all I think there is a misprint in  both _my_ manuals, and 
this is what causes the confusion They say the diameter of the spot 
is two-thirds of the short side of the viewfinder framelines for the 
lens you are using. Now that would correspond to a spot diameter of 
16 mm (two thirds of 24 mm). If that was true, then the 23% measured 
area is correct.

I measured the spot in  _my_  cameras by inserting a strip of paper 
just a bit larger than the diameter of the white spot. I then cut off 
a bit of the paper until it was as wide as the spot and then I 
measured the paper. Indeed it was 12 mm. As you can easily calculate, 
12 mm diameter approximates 13% of the film area. And one third of 
the long size. BTW, Réponses Photo also quotes the 13%, although they 
initially said that it only applied when 21 mm lenses were used.

Let me suggest you try out what is measured by doing a practical 
test. Put a sheet of white paper on a real dark wall and start your 
experiment by measuring only the dark area and set time/aperture for 
'correct' exposure. Use the widest angle lens you have as that makes 
it easier to estimate where the white spot is relative to the 
viewfinder frame. Then move in the direction of the white sheet of 
paper. If you move horizontally you will see that the red arrows in 
the viewfinder start moving once the white sheet of paper comes into 
the middle third of the viewfinder area. Now you know for sure what 
your light meter measures

Funnily enough, my manuals never mention 13% of the negative size, 
but it has a 1994 print date on the back. What date is your manual?

>I'm confused by something I read in the manual for my m6 ttl.  It says that
>the metering field is the 12mm spot, or 13% of the negative size, but then
>it also says that the metering field is 23% of what's in the viewfinder for
>any particular lens.  I think that means 23% of what's contained within the
>appropriate brightlines for the lens, which is confirmed by the illustration
>of the different metering fields for the different lens/brightlines.  Does
>that mean that the 12mm white spot somehow meters 23% of the field even
>though it amounts to only 13% of the 24x36 mm film size?  What am I missing?
>
>Mark
>
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Christer Almqvist
D 20255 Hamburg and / or
F 50590 Regnéville sur Mer

please look at my b+w pictures at:    http://www.almqvist.net/chris/new
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