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The techniques employed for panel balancing are not yet
adequate. At present an attempt is made to balance using full size apertures in
the projectors. This presents a broad white overlap on the screen making it
impossible to evaluate the equality of panel brightness and color. It is
also impossible to tell if vignetting along the matchline from any cause
is present under this condition. These are strong but incontrovertible
statements based upon the facts known to all optical trained persons familiar
with photometry. The division line between comparison fields must be as narrow
as possible.
Through the use of an undersize set of masks used in
conjunction with a full size set, improvement in technique is possible. These
masks can be made by putting tapes at the center of the overlapped area on the
screen and cutting the under sized masks to give a butt joint at this
position. Viewing should be done through a one inch wide slit cut in a black
cardboard held about at arms length so that only the areas immediately adjacent
to the butt joint are compared. Under these conditions equality of panes at the
matchlines is much more easily compared. The first time this is used, the
results will be surprising, particularly if a circular hole the size of a half
dollar is used to explore the butt lines from top to bottom.
To check on projector vignetting of the full sized
masks after the lamps are properly adjusted, the full sized masks should be
re-inserted and the flat mirrors adjusted again to yield a butt joint.
Vignetting if present will be plainly apparent.
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