[Leica] Viewfinders and the 2.5mm

[henningw at archiphoto.com (Henning Wulff)]

At 10:02 AM -0600 11/14/05, Jim Nichols wrote:
>That 2.5mm at the negative will translate into quite a bit more at 
>the subject's location.  I think that, with a sketch of the rays 
>connecting the subject to the image on the film, one could work out 
>a correction to the paralax settings on the Imarect finder that 
>would take into account the change in elevation of the finder above 
>the lens axis.
>Jim Nichols
>Tullahoma, TN USA
>

It doesn't work that way.

It translates orthogonally to 2.5mm at the subject, whatever the 
subjects distance. In other words, for any distance you're likely to 
focus your Leica at, it doesn't matter at all.

It's much more important to make sure that the finder is seated 
correctly, because any error in that translates into an angular 
error, which usually is significant.

The most common error is that the finder, especially ones without 
projected framelines, are vague enough or not accurate enough to give 
a correct idea of the field of view of the lens. Most finders without 
projected framelines are quite sensitive to eye position relative to 
the finder eyepiece, and this can make a huge difference. That's the 
most common source of error.

-- 
    *            Henning J. Wulff
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