ION 
ı to some more aspects of 
ise approach I do agree that 
uency response in optical 
ncy response in other phy- 
en very fruitful. It helps us 
anding of limitation in the 
s. However, I think we have 
ll the time against assuming 
ct. 1 feel the photographic 
from many of the electronic 
very often think. It is so 
ectronics that the amplifier 
er system is substantially 
andwidth in which you are 
1 can be constant and the 
e over the region you want 
gard it, therefore, as easily 
thing like the half-power 
ify the band width in a very 
in photography we are al- 
to the limits of the band 
lly interested in the region 
eginning to deteriorate, and 
ere, in the analogy, the gain 
id the phase shift is begin- 
it. To my simple mind, this 
ation much more difficult 
ay again that while CT tests 
ing for the future, I do not 
rn up all our resolution tests 
e no use. They are still quite 
perly carried out. We would 
y are low contrast tests they 
ection I am very interested 
Mr Bousky in the technical 
1gress, which is, in effect, an 
or low contrast testing. Mr 
cago Aerial Industries. 
p us to a better understand- 
| the limitations of our reso- 
should push on with them, 
e we can carry on with our 
anything we can do to im- 
n is well worth doing. 
9 take up the whole time I 
|, I think it is much more 
1er people should have a 
hing, so with the President's 
down and invite comments 
is subject. 
THE PHOTOGRAPHIC IMAGE, DISCUSSION 33 
Discussion 
Mr E. WELANDER: I have read Mr Brock's 
excellent paper with the greatest interest, and 
I am in full agreement with Mr Brock that the 
contrast functions will be a valuable aid in 
estimating the quality of the photographic image. 
In Sweden we have measured the transfer 
functions for some modern and some older air 
camera lenses. Further, we have multiplied the 
lens function by the function for the emulsion, 
the vibration, the image motion and the haze. 
In this manner we have calculated the function 
for the entire aerial photographic system. This 
predictive function has been compared with the 
function obtained directly from the air by pho- 
tographing a light ramp at night. It was from 
an altitude of 1,500 metres and I will show you 
this on a slide. [This slide is not reproduced 
here]. 
On the horizontal axis you see the frequency 
line and the vertical axis shows the contrast that 
the entire aerial photographic system will trans- 
fer. The line of dashes is the theoretically de- 
termined curve and the continuous line is the 
result obtained from the air; you see that the 
agreement is passable. The method has some 
limitations, we are studying them, but I think 
this could be stepped forward in studying these 
functions in practice. We have used plus X-film, 
/250 sec and velocity 290 kilometres per hour. 
I think the image motion is very important from 
this altitude. 
Mr P. D. CARMAN: Mr Brock has covered 
this subject so fully — at least in his printed text 
if not here verbally — that there is little left to 
say. I think the most useful thing I can do is to 
consider what we can learn from his text for ap- 
plication in the standard methods of testing 
cameras. 
It does appear that contrast transfer function 
is not ready for standard use yet. This leaves 
us with resolution testing. Our present recom- 
mendation, which was written in 1952, contains 
four different types of resolving power charts, 
and this number is certainly not desirable. In 
the comments which I have received in connec- 
tion with revising this recommendation, there 
have been some remarks along this line but 
there have also been some remarks suggesting 
that we needed yet other types of resolution 
targets. In general there was no consensus of 
opinion expressed on this subject and I have not 
felt it safe to make any change here. However, 
from Mr Brock's speech and from some other 
discussions and some other items I have heard 
about lately, I wonder if we really need to be 
this conservative. It seems to me that by now we 
have accumulated a lot of evidence to indicate 
that the high contrast resolution test is not a 
good test for photogrammetric cameras. Person- 
ally, I have felt that way for many years, but I 
have not wanted unduly to influence the recom- 
mendation. 
I wonder if the time has come to think about 
leaving out the high contrast resolution target. 
This would still leave us with three, which is 
more than enough, but it would be a step in the 
right direction, a step towards standardisation. 
I would like people to think about this pos- 
sibility between now and the time when we will 
be discussing again the recommendations for test 
methods, and at that time I would like to ask 
for a majority opinion on this subject. 
Dr F. E. WasHER: I too have read Mr 
Brock's dissertation on the subject of contrast 
transfer and find I am in general agreement 
with him, so that there is very little to be added 
to the line of discussion or comments on this 
paper. There are, however, one or two points 
which I think should be brought forward and 
thought about. 
In all this discussion on contrast transfer 
functions or transmission in photographic 
methods of measuring power, we should remem- 
ber what is the prime purpose of performing 
any of these tests. The prime purpose is first to 
evaluate the performance of the lens to be used 
and, second after having decided a lens is suit- 
able to mount that lens in a camera in such a 
manner that the maximum amount of infor- 
mation will be obtainable from the photographs. 
Any procedure that meets these requirements 
should be satisfactory. 
We hear too discussion about the type of 
target pattern, that too is more or less irrelevant 
because any type of target pattern that will 
establish a given photo plane should be suitable 
and satisfactory. In the course of an investi- 
gation carried out during the past year, I have 
found that the same focal plane is located for 
short lines, long lines or any other target. Like- 
wise the same one is located for high contrast 
or low contrast targets within the limits of air. 
This being so, it seems that much of our thought 
on these qualities provided us with a great deal 
of information on the performance of lenses and 
is one that we can say is now fairly well covered. 
Mr G. C. Bnock: There is not very much 
more for me to say. I noted with great interest