order to get more definition
ink we can take care of con-
at a later date.
nt is on image motion, and
r which suggested a rather
tolerable image motion than
6 — I suggested 0.3 — Mr
g a paper at this Congress,
ing paper on image motion
iis slide I indicate the results
me. Where the image motion
ition the image motion of
loss of resolution is 30 per
ures there, we have the per-
olution with various pro-
olvable distance in image
have indicated the tolerable
lifferent films of different
, under various values; the
inal 30 per cent of the re-
ling, for instance, for a film
illimetre, a tolerable motion
s. This is the basis of our
e Lands and Forests Depart-
f which you will see some
ind go a third of the way
« and allow 40 per cent,
and certainly not the 120 we
while ago.
nsert here a note on vertical
urposes of interpretation I do
ble to ask all the interpreters
lopes and terrains they have
:y see to what they know it
of probably 2.5 times for the
| overlap for the 6-inch lens
t that one sees a cube most
e when one puts a cube of
ffee. In other words, at the
of distinct vision we have the
y in the appearance of an
r distance it is indistinct, at
he disparity is less and there-
Consequently, I suggest that
on in aerial photography will
use a base to height ratio
iral one of the eye, base to
1ce of distinct vision or 1 : 4.
r natural appearance of an
vould see it if one were on a
ut as one would imagine à
ce of 10 inches from one's
e a ratio of 1 : 4.
| in normal 6-inch or 9 by 9
e we now use a 60 per cent
DISCUSSION ON PRESENTED PAPERS 41
overlap we should use 80 per cent overlap for
interpretation purposes, and use alternate pic-
tures for measurement purposes, I will show
you some of these a little later.
On the positive, these low density negatives
that I am proposing less than 1.2 alleviate the
printing problem, but we will still need contrast
control printers. However, I think they should
have smaller effective spot size and always a
continuously or nearly continuously variable
degree of control.
The choice of printing paper should be such
that it takes care of the contrast in the negative
within the spot size and not allow any of the
positive to become either black or white, or even
approach those — I was going to say gutless —
vicinities. What I mean is black and white are
the end points of information fade-out and must
be avoided in the positive if we are to retain the
information available in the original negative.
Now I would like to show you some slides
[not reproduced here] of targets we have pro-
duced not merely for the measuring resolution,
but other things which have been referred to on
several occasions during this Congress. Targets
we have constructed for testing some of our
cock-eyed ideas are shown here and these are
for measuring the actual variations we are get-
ting. In the upper half of the slide we have a
view from the ground of these targets, 160 feet
long, 16 feet wide, two tables. First in the lower
diagram you see a picture taken from 1,200
feet, and only a small part of the negative en-
larged indicates the general construction of the
target, with nine painted squares, giving a tone
smale, and on the left-hand end a black body.
This is 16 feet square and consists of 2,034
cells 4 inches by 4 inches by 12 inches deep,
painted glossy black, and we have not yet been
able to measure the reflection factor.
This, we thought, we would use almost en-
tirely evaluating the haze between the lens and
the ground. Having no light reflected from the
ground, the only exposure we get on the nega-
tive at this point would be due to light reflected
from the haze.
[Professor Jackson then gave some supple-
mentary slides.]
This is the last section on the last part of the
factors affecting interpretability, the methods of
Archives 4
looking at the pictures. We have reached the
point where we want a lot of people to look at
the same stereo pair at once and this is the pro-
jector kindly lent by the Overseas Surveys, it
is a projector I showed first in Washington in
1952 and has arrived here since then. I have two
slides made from contract prints, contact trans-
parencies mounted in 34 square slides and then
put in these lanterns. I can move the slides
across the screen, and if you take your glasses
off for a moment you can see what I am doing.
[The audience removed their special viewing
glasses provided by Professor Jackson.]
The arrow is not polarised and consequently
you see it with both eyes on the screen, and
wherever the image coincides on the screen
there the point seems to be. You may have an
idea that the arrow is going backwards and for-
wards, but actually it is the model that is going
backwards and forwards. This is a pair of pic-
tures taken by the method outlined with low
density in the negative, low gamma in the devel-
opment and high density throughout the posi-
tive in order to avoid blacks and whites.
This is forest photography on Ontario, scale
of 1:8,000 printed so that there is no white or
black. Those in the front row will be able to see
the beaver dam that crosses the gulley at this
point, and the beaver house just on the river at
that point. I might say that those who are beside
the lantern are seeing the photographs as if they
were using a 1.25 magnifier whereas those half-
way to the screen might be using a 2.5, three-
quarters of the way, 5.0, seven-eighths of the
way, 10, and we can see these pictures to ad-
vantage with magnification. Those beside me
are less fortunate.
This is forest photography on a larger scale
using 80 per cent overlap to avoid exaggeration.
This is at 1:8,000, and I think you will admit
that the vertical scale of those houses, cars et-
cetera is not as much as usual. I can show you
what the usual is by just changing the right-
hand photograph here, and this is a 60 per cent,
and finally, greater still.
I think that is about as much as I have time
for at this moment. I would have liked to have
shown one or two of the slides with respect to
stereo but I believe we have no more time.
