Another advantage of the additive source is that the
exposure change is incorporated into the same tape channel as the color change.
In the subtractive type the change is effected manually or by separate tape
controlled Robot system. A manual operation increases the chance of rejection
by greater than a factor of three, since an error in one panel results in
rejection of all three strips. Furthermore while a small error in a single
panel would not be serious, the same error in multipanel system is relatively
If further work shows that color and exposure balance
between panels cannot be maintained almost perfectly, the changeover to the
relatively expensive additive printer light sources is indicated.
Projection is the most serious source of panel unbalance in
terms of both illumination and color. It is so bad that it was found to be
completely impractical to attempt to balance the answer print on the basis of
screening in the theatre. Instead, three strip film projectors, filtered for a
visual match to arc light, and operated at average screen brightness were
pressed into service for this purpose.
Contributing factors to imbalance is projection include all
those mentioned previously, plus differences in lens focal length, (which
affects vignetting characteristics) differences in reflectance and color of
reflectors and mirrors and the usual fluctuations of the arc which can vary 10%
or more in a short period of time. In addition a gain screen will make one or
other panel appear brighter depending on seat location, making it imperative
that a perfectly matte screen be utilized. The solution to this problem is not
an easy one. As mentioned previously, it calls for a comprehensive development
program which will probably lead to considerable modification of lamps,
rectifiers, projectors and lenses.
The same basic pieces of equipment contribute to matchline
First, it should be noted that however perfectly the
matchline may be adjusted in the printer, the appearance is considerably
modified if for any reason the color and the brightness of the panels are not