For those who do not want the trouble of making the
niters, the Wratten & Wainwright gelatine film filters of
the requisite size may be bound up between glasses. The
numbers of their filters are, for the red No. 29 or F,
for the green No. 61 or N, and for the blue No. 50 or L.
A moment's consideration will show us that as we
want to reproduce the red, we must use a red-sensitive
plate, and it will be found more satisfactory to use panchromatic
plates for all three negatives, as by doing
so the gradation in the three negatives will be more
alike than when we use different kinds. There is some
latitude here, as we are able to modify the final result,
and one might choose a panchromatic for the red, an
isochromatic for the green and an ordinary plate for the
blue filter exposures; but it cannot be advised. Whether
a fast or slow panchromatic plate be used is of no particular
moment; the slow kind will give as good results
as the fast and is less likely to fog. At the same time
it must be borne in mind that we are making negatives,
not transparencies, and this must be kept in view in
developing. Brilliant-looking plates with clear glass
shadows are not the desideratum; but soft negatives,
rather thin in the high-lights, with fully exposed shadows,
should be aimed at. It is immaterial what developer is
used, and the beginner should use that to which he is
accustomed. Naturally the desensitizing process may
be adopted, and the plates should be backed.
In the reproduction of a screen-plate it is clear that
we might place it with the film in contact with the sensitive
plate. Then we should have the color elements
reproduced quite sharp, and every negative would be
broken up into minute dots corresponding in size. For
some positive processes this might not be a disadvantage,
but in the case of the separate system in which the positive
is bound up with a viewing screen, we cannot obtain
contact with the sensitive surface. The result will
be more or less want of sharpness, but this will not be
of serious moment, and it breaks up the screen pattern,
so that almost closed or continuous tone negatives are
obtained. Actually it is advisable to follow the same
plan with an autochrome, that is, to interpose between
the sensitive surface and the picture film a colorless
transparent medium of greater or lesser thickness.
There are some very simple mathematical formulas
by which we can tell not only what ought to be the thickness
of the intervening medium, but also the distance
of the light source, and the resulting want of sharpness
in the resulting negatives. But one of the main ideas
in this little book has been to avoid, as far as consistent
with clarity, mathematics and deep theory, so that it
will be assumed that it is required to make the negatives
from autochrome and Paget pictures.
E. J. WALL, F.C.S., F.R.P.S.
"The Dictionary of Photography,"
" Carbon Printing," etc.
AMERICAN PHOTOGRAPHIC PUBLISHING CO.
BOSTON 17, MASSACHUSETTS
COPYRIGHT, 1922, BY
Entered at Stationers' Hall
PRINTED IN THE UNITED STATES OF AMERICA
Electrotyped and printed, June, 1922
THE PLIMPTON PRESS
NORWOOD, MASS. U.S.A.