RBT/Spicer mounting issues (was Re: Mounting Gauges)

[P3D Paul Talbot <ptww@xxxxxxxxx>]

Thanks to Robert Linnsteadt for kindly clearing up my confusion
about Realist vs. European format mounting gauges.  Robert
wonders out loud:

> Is .3 mm getting too fussy?  I've mounted with the right gauge and the
> wrong gauge and cannot tell the difference on-screen.  But then, I may
> be seeing my slides through rose-tinted polarized glasses.  8-)

I have to say that .3mm makes a big difference for me!  I think I
understand why it doesn't for Robert, however.  (See the third item
discussed below.)

The reason I asked for an explanation of the difference between the
gauges relates to my continuing attempts to get the RBT jig/Spicer
mounting procedure to work satisfactorily.  While it has been going
much better with continued practice, I have observed a few problems
that I don't think can be resolved very well.

First, DrT mentioned that the apertures of the 5P Spicers seem to have
some rotation error.  What I have observed is that the perimeters of
a 5P Spicer do not "square up" precisely with an RBT.  Specifically,
if you hold an RBT and Spicer together, facing forward with the bottoms
on a flat table, the left (vertical) edge of the Spicer does not
align properly with the same edge of the RBT.  I'm not sure if
this is the same as, or related to, the rotation error that DrT
found noticeable.  Although I have not tried to correct for this
difference, in viewing my slides I have not had any discomfort
related to the edge alignment problem.

Second, the aperture of the 5P Spicers is taller than the aperture
of the RBTs.  Therefore, your vertical cropping will change when
you transfer the chips from the RBT to the Spicer.  This should
be a problem in relatively few circumstances, but you need to be
aware of it if you use the RBT/Spicer method.

Third, and most significantly, the windows of the RBT and Spicer
are not the same.  This has caused numerous problems in my attempts
to use the RBT as a jig for the Spicers.  When cropping close to
an edge of an image, one chip sometimes ends up with light leaking
past the edge after the transfer to the Spicer.  When cropping out
something close to the camera at the edge of a scene in the RBT, the
object may reappear and cause a window violation after transfer to
the Spicer.  When mounting very precisely to the window based on
the results as previewed in the RBT, objects will inappropriately
stick through the window, just as Robert's discussion of the gauge
differences predicts.  If you do not mount to the window (and I
seem to recall that Robert mounts to infinity), the 0.3mm difference
may well be insignificant, as Robert concluded:

> Practically, I don't think it will be a problem except in projection,
> and then only in situations which really push the limit.

I suppose you could call it "really pushing the limit" but I have
found that when mounting to the window for slides that will be
projected, it is critical to place the nearest object as close
to the window as is humanly possible.  If the nearest object is
the slightest bit behind the window, the stretch of projection
makes it look a looooonnnnnnggggg way behind the window.  IMO,
the visual impact of the slide is severely compromised in this
situation, so I have been taking the time to be painfully precise
with window placement.  Unfortunately, I get frequent problems "with
things poking through the window inappropriately" when transferring
chips from the RBT jig to the Spicer.  With no easy way to adjust
the window placement once the chips are in the Spicer, I have to
repeatedly transfer them back and forth hoping to get it right by
trial and error, or accept less than optimal window placement with
the slides I mount in Spicers.  (I cannot see enough detail in the
chips on the light box to mount to the window by a gauge alone.)

I still think the RBT jig/Spicer procedure is a great way to save
on out-of-pocket costs for mounting.  But there are some inherent
obstacles to precision mounting that must also be considered.

Paul Talbot, reporting from the mounting trenches


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