30 THE PHOTOGRAPHIC IMAGE, BROCK
Grey base (2s distinet from a disappearing anti-halo coating) would have the dis-
advantage of increasing the opacity to the printing light, a drawback especially for
electronie printers. This could be minimised (assuming a blue printing phosphor) by using
a bluish base, which in conjunction with the minus blue camera filter would be effec-
tively black.
6.2.0. Standards.
Sensitometric testing procedures and standards are not agreed, even among military
agencies. It is highly desirable to establish international standard tests for such as speed
and spectral sensitivity, and probably even the controversial resolving power. Without
such agreements reviews such as the present one are difficult to write. In this case
speeds had to be quoted on a relative basis for lack of a generally agreed standard which
has any meaning in the conditions of air photography. It is often contended that sensito-
metry cannot be made to give satisfactory agreement between different laboratories
over long periods of time. While it is true that precise agreement is difficult to obtain,
experience over some 12 years in Great Britain has shown that two industrial and two
government laboratories can keep in reasonable alignment. Speed measurements do not
differ by more than = 0.05 log units, and this order of accuracy is quite sufficient for
placing emulsions in one category or another. In the past far too much research effort
has been expended on relatively trivial matters concerned with interpretation of the
characteristic curve but for photogrammetry simple standardised tests closely related
to conditions of use can readily be devised.
Acknowledgments.
A first draft of this paper was given a limited circulation in autumn 1959. Some
recipients made valuable criticisms and comments, and in revising the present version
account was taken of these, so far as was possible in the time. I would especially
acknowledge the comments of:
Professor Ingelstam, Institutet fór Optisk Forskning, Stockholm.
Professor Maréchal, Institut d'Optique, Paris.
Mr. E. W. H. Selwyn, Research Laboratory, Kodak Ltd.
Mr. J. A. Eden, Directorate of Overseas Surveys.
During the writing and revision of the paper I have had many useful discussions
and arguments with Dr. P. M. Barham, Air Photography Division, Royal Aircraft
Establishment.
The emulsion threshold curves of Fig. 7 (and several others) were measured by
Mr. P. G. Powell, of Kodak Research Laboratories, under a Ministry of Aviation
contract.
Professor Ingelstam supplied the CT curve for the 6" f/5.6 lens of Fig. 6.
Other curves have been taken from the publications of Washer (1) (Figs. 9 & 16);
Lindberg (2) (Fig. 10); Sproson (3) (153 mm, f/2 lens, Fig. 6); and Blaschke (4)
(60 mm, f/2 lens, Fig. 6).
The emulsion CT curves of Fig. 11 are based on data supplied by Mr. Raife
Tarkington of Eastman Kodak Ltd.
Acknowledgment is also made to the Proprietors of “Punch”, for Fig. 1 and the
Editor of “Wireless World” and M.G. Scroggie for Fig. 5.
References.
There is now a very big literature on frequency response or CT testing, and the
preparation of a representative list of references would in itself be a formidable
undertaking. Those who wish to read further will find useful references in some of the
papers |
survey |
[1] Wi
[2] Li
[3] Sp
[4] Bk
This
contains
of paper
The
photogr:
frequenc
much m:
can prol
aerial pl
involve ;
which is
formanc
Frequen
automat
use to tl
The
cussed.
Refe
quality.
First of all
printing errors
in “Photogramr
saw any proofs
before the thin;
errors will be
derstand what ‘
I do not war
what I have alr
sibly I have sai
save time is t
thoughts which
this question :
testing. I do wi
speaking — and
speaking — fr
quency respons
surements. This
about but in m
measure. À gre
best of my knc
ground of meas
we use in phot:
