P3D overlap and RBT X4

[Rod Sage <rsage@xxxxxxxxxxxxxxxxxxxx>]

Alan Mahon wrote
>I have a modern equivalent of the overlapping problem and would
appreciate
>any opinions others may have.  After a 2 year wait I acquired an RBT X4
from
>the manufacturers earlier this year.  This is a pair of Cosina SLRs
spliced
>together by RBT.  They make a number of other spliced pairs based on
Ricoh
>and Yashica bodies.  There appears to be a design fault which causes
>overlapping images.  Its specification is full-frame 35mm with a stereo
base
>of 75mm.  Between the two apertures there is space for one frame.
Having
>exposed a pair of images the camera advances one frame (8 perforations
or
>38mm).  After the second pair is exposed the camera advances three
frames
>(24 perforations or 114mm) and so on.  The separation of the apertures
>should therefore be the equivalent of two frames or 76mm so that images
are
>evenly placed along the film.  The choice of a base of 75mm therefore
seems
>incorrect and to make matters worse mine is nearer to 74mm.  I get
spaces
>between images of 2, 0, 2, 4mm repeating.  The consequence of this is
that
>processors have declined to mount slide film and they object to
printing
>from negative film because they say that their equipment needs a
consistent
>gap to find the edge of successive images.  I know mounting stereo
slides is
>not ultimately a problem because the widest recommended mount has an
>aperture of 33mm but why not set the base to 76mm to be consistent with
an
>advance of 8 perforations (or 38mm)?  I have emailed RBT and reminded
them
>but can get no reaction from them so their philosophy is a mystery.

If the lenses (aperatures) are closer together than the 76mm of two full
frames, it could be to adjust for the stereo window.
Have you measured across the film plane?
If there is a spacing problem you probably need to ask for slides uncut
and mount them yourself. The widest Realist type mounts are about 33mm
wide anyway. If you are looking for pre-mounted slides for 2x2x2 viewers
or projection there would be a problem. Any lab should be able to easily
make prints and you could trim them slightly. Often you loose a bit of
each image on a print anyway.
RDS