P3D Re: On Film Deviation

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

>Since the OFD depends on film size, what feature of the film
>size does it depend upon?  The height, width or diagonal?  Since the OFD
>is basically measuring a change in the horizontal direction, is it 1.2mm
>for a frame 36mm wide and somewhat less for the frame size of a Realist
>camera?  What, for example, should the OFD be for a Nimslo half-frame
>camera?

Very interesting questions.  It is my understanding that maximum on-film 
deviation should be proprotional to the width of the film and it is better
expressed as a percentage of the image width. 

HOWEVER, the restrictions on maximum OFD have been imposed mainly by 
projection, so as long as different widths are projected mixed up (same 
screen, same magnification) I believe the maximum OFD should be the same 
for all pairs mounted in standard stereo mounts.  So, I would use 1.2 mm 
maximum OFD for Nimslo images.  The reason the maximum OFD for medium
format is larger has to do with the fact that less magnification is
required to project MF images.  If a MF pair is mounted in 35 mm mounts 
and mixed up with 35 mm pairs then we are back to 1.2 mm.

ALSO, I consider the 35 mm lenses in a Realist to be wide-angle even
though they are "normal", being equal to the diagonal of the frame.
For the same reason that a full frame pair taken with 35 mm lenses
and cropped to Realist size is still wide angle in my eyes.

George Themelis



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