Re: "Perfect" slide mounting?

[P3D <PTWW@xxxxxxx>]

I heartily second Gabriel's thanks to DrT for the thorough explanation
of mounting/projecting issues!  I too have been mounting slides for the
first time this past week.  While I was comfortable with the distinction
between mounting for constant infinity and mounting for the window for
viewing with a viewer, I was unclear whether projection raised additional
concerns.

If I understand DrT's explanation correctly, it seems that once the slide
frame has been aligned for the first slide, the horizontal control should
not have to be adjusted again.  Having watched slide projections where
a slide appears with the mask's edges out of alignment leads me to wonder:
what would cause this to be so?  It appears one explanation is that for a
previous slide, the projectionist (incorrectly) adjusted the horizontal
control to reduce ghosting, and I did not notice that the mask's edges
were out of alignment as a result.  Are there any other possible conditions
to cause this problem?  I'll hazard a few guesses, all theoretical, and
look for "real-world" feedback from the list:

    -- Inconsistencies in the production of the slide mounts;
    -- Differences among mount opening sizes--e.g. 5P vs 7P
        (my guess is this is *not* an issue if the openings are
         consistently centered properly);
    -- Differences among mounts made by different manufacturers;
    -- Imprecise masking down of a mount to a different opening size.

Any theoretical validity to these guesses?  If so, how common are these
problems?  Are there any other possible causes of mask misalignment
between successive projected slides?

I thank you now for your feedback...and your eyes may thank you later!

Paul Talbot


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