Re: [Leica] M6 Wide Angle Body = reduced vf magnification?

[John Collier <jbcollier@home.com>]

I am not much of an optical wiz but one of the things I like about this list
is that fools seldom suffer in silence :-). I find I learn just as much from
the corrections of my mistaken (though, I assure you, well intentioned)
attempts at explanations than I do from my own questions. So here goes.
Putting a lens in front of an optical unit ( i.e.: rangefinder, lens, eye),
not only changes the field of view (the primary intention of the goggles in
this case) but also the position of the plane of focus of the optical unit
(focal point, I think). A simple example of this is a close up lens for a
SLR lens. If you change the focal point of the camera's rangefinder system,
then a different profile lens coupling cam would be required to compensate
for this.

John Collier

> From: Skip Williams <skipwilliams@pobox.com>
> 
> OK, OK, now I'm in over my head.  I have just enough knowledge to be
> dangerous.
> 
> Why do you have to change the profile on the focusing cam when you put on
> the spectacles?
> 
>