Archived posting to the Leica Users Group, 1998/05/25

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Subject: [Leica] Retrofocus Lenses
From: Marc James Small <msmall@roanoke.infi.net>
Date: Mon, 25 May 1998 23:23:42 -0400

At 07:34 PM 5/25/98 -0700, Bryan Willman wrote:
>The real point here is that Retrofocus lens is
>physically longer than its focal length.  So,
>a 21mm for an M camera must be retrofocus,
>since you can't fit the nodal point within 21mm
>of the film plane.

It's the other way around.  A 21mm lens for an rf camera, such as the M,
CAN be non-retrofocus, as you can design it readily so that the rear
element is easily within 21mm of the shutter curtain/focal plane (yeah,
yeah, there are two or three mm here, I realize!).  But you cannot design
such a lens for an SLR, and leave space for the mirror, which takes 35mm or
so of depth.

Reverse telephoto wide-angle designs were first made by Carl Zeiss
immediately prior to World War II but were first popularized by Angenieux,
who coined the trademark "Retrofocus" for such formulations.

Marc


msmall@roanoke.infi.net  FAX:  +540/343-7315
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