P3D Re: Mounting Guages

[aifxtony@xxxxxxxxxxxxx (Tony Alderson)]

>Andrea Blair wrote (digest 2780):
O.K., I know I've been successfully competing and showing 3-D programs -
but I'm *still* confused about the mounting guages (purchased from Reel
3-D). I have read several different instructions on which ones to use when.
I use 5p and 7p Albion aluminum masks (less and less) and 5p and 7p RBTs
(more and more). Do I use the 5p gauge for 5p masks and 7p gauge for 7p
masks or do I use the 5p guage for both sizes? What about close-up or half
frame masks? And the other assorted sizes of RBTs? HELP!! I want the most
accurate mounting so there is little need for adjustment during shows.<

Well, I'm the guy that drew those pesky Reel 3-D gauges, many, many, MANY
moons ago, so maybe I can offer a little insight.

The reason there are different gauges for the 5P and 7P formats is that the
masks have different center spacings.  So if you used a 5P gauge for a 7P
mask, you would set the infinity point incorrectly.  The Reel 3-D gauges
were designed for the Realist/EMDE masks, whether they are appropriate for
the Albion and RBT mounts depends on whether the mask centers are the same.
I don't have any of those mounts on hand, so I can't check it for you, but
Mark Damish's suggestion of checking the mask edge with the near markings
is appropriate. If you're interested, Charlie Piper detailed the Realist &
EMDE mask dimensions in The Technical Page #72.

>Dr. George A. Themelis wrote:
Andrea, good luck figuring out the gauge. I have never used one... The
mount itself (any mount) is the best gauge I have available (see Piper for
more on this). I mount to the window and with a bit of concervatism when
shooting I don't have problems.<

If you're using a "standard" stereo camera, and restrict your depth range
appropriately, I agree the parallax guide on the gauge is somewhat
redundant. It's easier, and more effective, to mount to the window, rather
than to infinity. However, the horizontal lines can be useful in checking
for vertical and rotation errors--even if your camera is accurately
aligned, there is some slop in the masks. The gauges are most useful when
mounting slide bar, shuffle and twin camera shots, which often have
alignment errors or excessive parallax.  The gauges are also very helpful
when cropping the stereo slide.

>and from Michael Kersenbrock:
>>twin cameras, align the near points, and make sure that the distant
>>points aren't too far apart (beyond the far-line) for projection. <<
>The real question comes when the the distant points *are* too far apart,
>but you really love the potential image and don't want to toss it.
So does one "make sure" or does one "pray that"?<

Ah, well this is where we separate the butterflies from the caterpillars in
stereo mounting! ;-)  Of course, the "best" solution is to plan out one's
photography so that the parallax is suitable for projection. But things
don't always work out that way.  The only way I have found to save such
slides is the method Ferwerda calls "double depth." Basically, you have to
make a custom mask with closer center spacing (by slicing a thin strip out
of the mask and taping the halves back together). This will give you a
stereo window that is floating off the screen. So now you can use the
theater space to accomodate the excessive parallax in the image.  The gauge
is essential to insure you don't exceed the maximum for infinity (and to
make the  custom mask).  Do you understand? In other words, you mount to
infinity and then float the stereo window forward to accomodate the near
point. Needless to say, this is a LOT of work, so the slide better be
doggone good before you attempt this save.  Furthermore, this gag only
works if you KEEP YOUR MITTS OFF THE HORIZONTAL ADJUSTMENT DURING
PROJECTION! If some well-intentioned fellow pushes the window back to the
screen during projection, he will push your infinity points to divergence.

Tony Alderson
aifxtony@xxxxxxxxxxxxx



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