P3D Realist image size distortion

["KENNETH LUKER" <KLUKER@xxxxxxxxxxxxxxxxxxxxxxx>]

I've encountered a very unfortunate problem with my Realists:  
Probably due to insufficient lubrication of the sliding surfaces 
between the moving back-plane and the camera body, the rear 
plane holding the film doesn't always move evenly during focusing.  
I would have thought that the springs holding the back-plane in 
contact with the focusing cams would have kept the plane in 
alignment, especially since they are helped by pressure from the 
pressure plate.   But sometimes the back-plane sticks, leaving one 
end at a different distance from the lens than the other.  As a 
result it becomes tilted with respect to the optical axes.  

Normally you might expect this to result in one of the views being
focused and the other not in focus.  Since I usually shoot at f11 or
f16, both views are usually in focus, but the difference in distance
from the lenses causes the images to be of different sizes. The image
recorded closer to the lens is smaller than the image recorded at a
greater distance.  I was surprised at how sensitive the image size
is to variations in the lens-to-film distance. There are undoubtedly 
other distortions present, such as slight keystoning, but the size 
distortion predominates.

I first noticed this image size difference during mounting.  I 
despaired, thinking that the lenses were mis-matched in focal length, 
which problem would have had the same symptoms.  But I found that the 
problem varied from roll to roll, being absent on some rolls, and 
worse on others.  My practice had been to mount to the bottom edge of 
the mount, letting the upper edge fall where it might.  I found that 
on views that have greatest size distortion, the image with the 
smaller size has much more image showing at the top edge than the 
other image shows.  If I mount to the center (putting the center of 
each image in the center of its mask), then I have apparent mounting 
errors on both top and bottom edges.  In the worst cases, the views 
can't be viewed comfortably, regardless of mounting choice.  The eyes 
try to make the views congruent, but the size mismatch makes the eyes 
feel as though they were in a vise.   

Has anyone else had this problem with their Realist?  (I've noticed
it now on at least two of my four Realist cameras.)  It is easily
detected on projected slides, by superimposing the projected images
and comparing the vertical size of corresponding elements.  And do
you know just where to lubricate to ensure that it gets cured? 

Ken Luker_______________________________________________________________
Kenneth Luker
Marriott Library Systems and Technical Services
KLUKER@xxxxxxxxxxxxxxxx


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