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 errors.

    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 perfectly balanced.