Archived posting to the Leica Users Group, 2012/07/21

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Subject: [Leica] Some technical speculations re: rangefinder
From: wildlightphoto at earthlink.net (Doug Herr)
Date: Sat, 21 Jul 2012 20:25:42 -0700 (GMT-07:00)

Herbert Kanner wrote:

>Wow! That was something I was not aware of and had me going for a 
>while. Then I started thinking about it like the physicist I once 
>was. I said, ok, when you get closer, the lens has to move away from 
>the sensor/film. Now think about a pinhole, which could be thought of 
>as an highly stopped down lens. As the pinhole moves away from the 
>film/sensor, the angle subtended by same becomes smaller. So the 
>frame lines in the viewfinder should get closer to each other, making 
>a smaller rectangle.

Yes that's how it works for a lens that focusses as a unit.  Internal focus, 
front-focus and rear-focus designs complicate the matter.

Doug Herr
Birdman of Sacramento
http://www.wildlightphoto.com