Archived posting to the Leica Users Group, 2000/03/20

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Subject: Re: [Leica] Re: Leica Users digest V16 #54
From: "Henning J. Wulff" <henningw@archiphoto.com>
Date: Mon, 20 Mar 2000 18:49:36 -0800

At 10:43 AM -0800 3/20/00, William Carson wrote:
>Regarding "Film Flatness":  It would appear that the people at Franke &
>Heidecke in Braunschweig encountered the problem of "film flatness" quite
>a long time ago in
>their engineering of the Rollei cameras.  At least two models of their 2¼"
>square format reflex cameras [I owned a Rollei flex F and also a
>Tele-Rolleiflrx with
>this feature] offered optical flat glass plates located in the image
>plane, ahead of the film, to offset the tendency of the 120 film to "bow"
>or "buckle-out" in
>it's location in the aperture of the image-making portion of the cameras.
>It appears that the pressure plate by itself in a single plane did not
>correct the
>geometry of the film in this critical area.  It is reasonable that the
>film would present a very flat surface to the image with this feature.  I
>do not know that
>Hasselblad ever offered such a feature although it is certainly reasonable
>to assume that their engineers would aware of this design?  Bill Carson,
>KE7GM@earthlink.net

Yes, Hasselblad has offered such a thing, in the form of a Reseau plate in
their MK70 and MKW cameras. These are their photogrammetric models for use
with special versions of the Biogons of 38 and 60mm focal length and of the
100 Planar. This plate (a calibrated piece of glass ahead of the film
plane) serves two purposes; one, to hold the film perfectly flat and two,
it is etched with fine crosses to allow the negs and prints to be measured.
When you buy one of these cameras, you get a detailed report on the
geometry of the whole camera, including an exact report on the distortion
remaining in the lenses and the remaining curvature in the film. Film used
is not 120, but 70mm because it can be held more precisely than 120 film.
Among other things, these cameras are used in my field, architecture, to
allow production of as-built drawings of older buildings which might
otherwise be hard to measure.

   *            Henning J. Wulff
  /|\      Wulff Photography & Design
 /###\   mailto:henningw@archiphoto.com
 |[ ]|     http://www.archiphoto.com