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«tion of the 
produced, 
but not in Great Britain, and the demand for this type of sensitising 
does not appear to be increasing. 
The writer maintains his conviction that a sensitising for deep 
red and near infra-red would be ideal for general use in air photography 
to replace the present panchromatic type, but so far no such emulsion has 
been produced with the same working speed as the Class L panchromatic. 
=. PRINTING 
Bromide* Paper Characteristics 
It has been well-known for some forty years that in printing air 
photographs the best results (defined as the maximum transfer of informa- 
tion from the negative) are obtained by making "soft" prints, i.e. avoid- 
ing any near approach to white paper or the maximum density which the 
paper will produce. Nevertheless there is a marked resistance to making 
prints of this kind, and in particular to using the so-called "soft" 
grades of paper. In the writer's experience of prints produced for use 
as distinct from research the majority are much too contrasty, with 
serious loss of the total information in the negative, and although soft 
papers are provisioned they are hardly ever used. Why does the practical 
photographer so consistently pursue an apparently illogical course? 
One reason is obvious: a print of the desirable type is so much less 
attractive to cursory examination by unskilled eyes. The difference 
between the best print and the superficially attractive print varies 
according to the subject and the scale, but in many cases it is very 
great, and the print which is acceptable to the research worker would 
often be rated as absurdly soft by others, who do not necessarily 
examine it under magnification. In some photogrammetric applications, 
it may be preferable to reject most of the information in the negative 
for the sake of improved ease of seeing outlines. Nevertheless, there 
remains a large area of use in which the totality of information is 
important, yet in this area the worst prints are commonly produced. It 
is worth seeking technical reasons for this state of affairs. 
In this context the extreme densities which we should avoid are not 
significant in themselves but only for the gradients which they connote, 
especially since the user of air photographs is free to study small areas 
individually and to illuminate them to any level he pleases. Fig.2 shows 
the characteristic curves of typical soft and contrasty bromide papers 
and on the same diagram are plotted the curves of gradient against log 
exposure (the first derivatives of the characteristic curves). Clearly 
we cannot print the whole range of any negative at a constant transfer 
gradient, and the choice of any particular paper grade will always be a 
somewhat arbitrary compromise. If we wish the print to look bright and 
attractive at a distance we might choose the contrasty grade, which in 
the example shown would use almost the full density scale of the peper. 
  
* 
The word "bromide" nowadays signifies only a speed class and many 
papers in this class are dye-sensitised chloride or mixed halide.