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While several techniques are available to partially overcome
these emulsion characteristics they would require in practice require scene to
scene programming which these printers cannot do without complicating them
almost impractically. The best that can be done is to introduce the correction
most required in the roll as a whole. In this picture a 2½ yellow or a 5Y
filter is removed from the feather filter packs to reduce the blue shift for
rolls where blue skies predominate.
Matchlines also shift toward the blue if film is stored
overnight after printing and before processing. This requires removal of a 2½ Y
filter from the feather packs if the storage period is a day or two. If storage
would continue for nearly a week, a 5Y filter would have to be removed. This
correction is in addition to the blue sky shift.
The characteristics of the masks are such that they yield a
good linear blend line over only a narrow exposure range in printing. Since
exposure is controlled by lamp voltage the range can be expressed as about 4 volts
on AB and about 6 volts on BC. At very low voltage the feather looks like a
white line between the dark lines at its best and the condition reverses at
high voltage. This would give a means of correcting in part for some emulsion
characteristics just mentioned, if filter changes could be automated easily.
The AV mask has a small range because of a stop in its density wedge so that at
the high end of the exposure range two dark lines appear in the center of a
light band.
Since the feather is an optical wedge, increasing the
exposure moves the feather more into the picture and decreasing it moves the
feather out.
At the low end of the exposure range, it is a characteristic
of these particular masks that they do not completely opaque the print in the
region beyond the actual feather. Therefore, on very dense scenes a broad light
band may be seen corresponding to the total overlap of the projector fields.
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