se to use whatever 
er XX or the Ilford 
e entire framework 
emulsion which will 
e standards will no 
ifferences in thres- 
cts, and in such a 
one manufacturers 
wever, we are faced 
different emulsions, 
ution. How can con- 
ture of an obsolete 
a different kind of 
sting again from a 
or more than a few 
sation impossible. It 
e limiting emulsion 
high performance. 
the highest quality 
experience of these 
ifficient care taken 
1 within reasonable 
ic operations seems 
be examined under 
| certain amount of 
. change of size. In 
yduction, where the 
thin a known size 
nd better to specify 
1 and even a speci- 
and form of illumi- 
; of agreeing on a 
'esolution" are well 
herent difficulty of 
ptotic curve reaches 
limit the precision 
a rather low order. 
using long line tar- 
nsitometry to esta- 
elation between con- 
as not, apparently, 
reat attractions, but 
frequency response, 
ter solution in the 
, test. survive? 
| views on the reso- 
THE PHOTOGRAPHIC IMAGE, BROCK 25 
lution test, can we now determine its future? In attempting to do so we must speak not 
only (or even mainly) for the research worker, but must also consider the needs of stand- 
ards agencies, Government Departments, industrial laboratories, and those air survey 
firms who wish to test own cameras and materials. Will the contrast transmission method 
displace the resolution test everywhere, or will the latter continue to be used by some or 
all of these organisations? 
The writer believes that the resolution test will survive, though with a wider appre- 
ciation of its limitations. It does not give a full picture of the system performance, but 
provides valuable information directly related to practical air photography. Probably 
no other test could tell so much in so compact a result with less experimental effort. It 
requires a minimum of equipment, not beyond the resources of any of the organisations 
mentioned, and no skill which would not normally be found in such laboratories. It can 
only be standardised in a limited way, but enough for individual laboratories to grade 
cameras and emulsions for their own purposes. 
The contrast transmission principle of testing is well established in the television 
world, but in quite different circumstances. No equivalent to the photographic resolution 
test was possible, nor would it have conveyed any useful information. A frequency res- 
ponse function was essential to tie the lens performance in with the rest of the system. 
The complication of apparatus required for frequency response measurements was not 
excessive in relation to that already in use. Nevertheless the diversity of methods em- 
ployed, and the continual development, indicates that practical problems have still to 
be overcome. These problems will certainly be no less in the application to photography, 
where the important frequencies are decidedly higher. The emulsion contrast transmis- 
sion is an additional problem, and questions relating to nonlinearity have yet to be 
settled. The standard of skill required will be higher, and not necessarily available 
except in the larger laboratories. Much greater care will be needed in handling photo- 
graphic materials. (The eye is remarkably efficient at separating the relevant from the 
irrelevant, and will assess a resolution end-point unperturbed by a mass of flaws and 
scratches, which are all impartially recorded by a microdensitometer, rendering the 
advantages of “objective” measurement somewhat illusory.) Interpretation of results 
will be even more difficult than with resolution tests. The latter, after reduction, provide 
a set of points representing performance at various apertures, angles of view and focus 
positions contrast transmission methods will replace every point by a curve. The digestion 
and presentation of this mass of information will be a problem in itself, which is un- 
likely to be solved in the near future contrast transmission equipment is much more 
complicated, and to that extent standardisation may be even more difficult than for 
resolution testing. 
Contrast transmission then, will provide much more information than resolution 
tests, but will require correspondingly greater effort to obtain and assimilate it. The 
results will be valuable, if not essential, to lens designers, and for research work gener- 
ally, but the methods are not likely to be widely used. This may be altered if there is a 
strong pressure for standardisation of testing by means which eliminate changing film 
characteristics. 
The future should therefore see the continuance of the resolution test for general 
use, and there should be some attempt at standardisation contrast transmission testing 
will grow, as an essential for the full understanding of image phenomena, but it will be 
restricted to the larger laboratories. 
5. Tests of airborne performance. 
Although this paper is concerned mainly with indoor studies of camera performance, 
the ultimate test, which includes all factors of the airborne system, must be done by ac- 
tual air photography. While it is possible for experienced people to make very good judg- 
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