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With extended density range and appropriate gradient in the paper,
we could then print a given negative at a higher overall gradient, without
risking loss of fine detail. This, in effect, is what can be done with
the improved modern papers, which have an extended density scale as com-
pared with those available some years ago. Their superior "quality" can
in fact be usefully employed in air photography without contradicting
the injunction to avoid extreme densities. It also follows that the
characteristic curves of all paper grades should have the same basic
shape; this unfortunately is not always the case. In general soft
papers tend to shoulder earlier than the more contresty grades, in
addition to having lower maximum densities. Now if the limiting density
is judged on the criterion suggested above it will be found that the
useful exposure scale of many soft papers is little if at all greater
than that of the "normal" papers in the same series. Some soft grades
of less reputable make shoulder at such a low point as to rule them out
altogether. Such papers are "soft" because they produce soft-looking
prints, not because they have a truly extended scale of gradation. If
contrasty air negatives are printed on them reproduction of a sort is
obtained, but it is inferior in the shadow region. It is suggested that
unfortunate experiences with soft grades of paper account for the resis-
tance to using such papers at all and also, by association, to making
"soft prints" on paper of any grade. In making soft papers for air photo-
graphy the aim should be to keep the maximum density as high as possible
and preferably to make the gradient increase with density; this is the
exact opposite to what often happens at present.
If we accept this progressively increasing gradient it follows that
with soft papers the gradient will be less than unity over an appreciable
part of the density scale in the highlight region. It is found, however,
that gradients down to about 0.5 (which is approximately 0.25X gamma in
many cases) can usefully be employed. The suggestion is tentatively made
that the useful exposure scale of bromide papers should be determined by
the densities at which the gradients are respectively 0.25X gamma and
0.9X gamma. (The inflection point itself is difficult to locate
precisely.)
The characteristics of some soft papers of different types are shown
in Figs.3 and 4. The characteristic curves of Fig.3 differentiate the
papers into a poor type (C), a typical soft of good make (B), and an un-
usually good example (A). Paper (C) is seen to have in full measure the
bad properties of tow maximum density and early inflection; paper (B)
exhibits similar tendencies but to a lesser degree, while paper (A)
approaches much more closely to the desirable characteristics. The upper
and lower limits of useful gradient determined as suggested above have
been marked on the characteristic curves and also on the curves of Fig.4.
Some relevant sensitometric figures are given in Table 3.
The ordinary Bar-Gamma is a guide to the contrast of the papers as
normally evaluated; on this criterion they are similar though not identi-
cal. The useful scales of papers A and B, as limited by the Bar Gamma
method, are similar and greater than that of C, but the spurious softness
of C is more clearly brought out in the third line of the table. Although
paper À is the most contrasty of the three, in the sense that its gradient
GE 5S pr roc SES ES PAS — :
