Converging cameras...

[P3D <LeRoyDDD@xxxxxxx>]

Catching up on recent digests after being away for two weeks...

     The only reason to converge cameras is to not have to mask the on-film
image at the sides.
     If one is using 8 perf 35mm @ 36mm width, the widest mount available is
33mm so image anomalies at the sides can be masked in mounting.
     If doing something close-up with twin 35s(under 7-10 feet!) it's better
to accept the image anomalies and mount in the narrower width mount as needed
to eliminate them.

     Keystone distortion is the common objection to converging, but my
opinion is that if keystone is large enough to be objectionable the stereo
base is far to great, anyway.
     My problem is that convergence can quickly give unmanagable image
disparaties in the shot.
     I did some wide-base "rock and run" telephoto shots at NSA Rochester of
the Kodak building and the sculptures on a couple of the buildings. The
200-300mm framing and the 20-50ft separation did fine with the subjects, but
I'm the only one who'll see these.
     I'd centered the subjects in the viewfinder making the clouds in the
background diverge. I might be able to salvage the images by cropping to 4
perf, but next time I'll use one of the most distant objects as an aiming
point or frame the subject left and right so as not to converge.

     Prism closeup attachments have the same problem... I've a great
instantaneous Teco-Nimslo shot of a butterfly in mid-air except there's an
out of focus cloud in one frame and only blue sky in the other.

     There's one type of shot that must be converged(so I'm told... I don't
know what happens when you don't!). A single camera(slr) closeup/macro with
 edge diffusion(vaseline or special purpose filter).
     I'm guessing that the convergence lets the diffusion "lay down" on the
scene that's not at the plane of the main subject evenly without any depth
effect in the diffusion itself.

LeRoy Barco
LeRoyDDD@xxxxxxx


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