At the high end of the exposure range, flare in the feather
optical system begins to be a problem, resulting in extreme cases in a broad
dark sharp edged band considerably wider than the matchline but narrower than
the overlap of the projector fields. There are no examples of this in the
picture since the region is carefully avoided. These are the major appearance
changes in the quality and color of the feather as a function of exposure
changes or changes in background.
Changes in feather quality can occur in maintenance if the
lens focus is altered, an imperfect filter is introduced between the film plane
and the feather mask, if the feather mask holder is imperfectly seated on its
pins, or if the mask falls off its holder and is not recemented properly. None
of these effects occur in release prints.
Color and exposure changes in the matchline occur also with
changes in the filter packs. The worst offender was the orange Eastman base.
This was avoided by change to a 2/3 nominal thickness of Corning Signal Yellow
glass. Avoiding the denser filter values helps by reducing the absorption of
energy in any one filter. The use a single glass in the carrier helped to
reduce buckling of the filters toward the lamp where they would be heated more,
leading to progressively faster deterioration or burning. The almost colorless
ultraviolet filter can also be left out inadvertently leading to an
orange-yellow shift. Improvement would come from use of all glass (not plastic
or gelatin cemented in glass) filters whenever possible, and redesigning the
lamphouse to remove the filter packs as far as possible from the lamps in
regions where the energy density is low.