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though we would like to have it more strict than we could make, it has worked 
rather well. At least, these specifications have had a uniforming effect in the meth 
ods of camera and lens testing. I should like to make a few amendments to the 
existing specifications. This draft for testing methods supplies information about 
two groups of data; one group is »definition of the qualities of the image», and the 
other group of data defines the »geometrical accuracy». As to the first group 
of information, the image quality, this is at the moment defined by means of the 
resolution. We know that the justification is not a physical one but it is a purely 
pragmatic necessity to use this measure as a means of comparison, and to 
standardize all circumstances when we determine this resolution. We also know 
that at the moment a better insight in the phenomenon of image information, 
image sharpness, is being gained. And we hope that in a not too distant future 
image sharpness can be defined in a stricter way than it is possible today, that 
it can be well defined in plain physical terms. I therefore propose that we leave 
the paragraphs regarding resolution unchanged for the time being. They will 
have to be changed, and be brought uptodate at some future occasion. The 
paragraphs regarding image illumination, shutter efficiency and veiling glare 
provide good standard methods and they fulfil also future needs. 
Now we come to the second group of measurements defining geometrical 
accuracy, i.e., the determination of the elements of inner orientation of a photo- 
grammetric camera. I have two amendments to these measurements. The first 
is the controversy between photographic methods and visual calibration 
methods. So far, many institutes are still using visual methods, other institutes 
use photographic methods. Having modern cameras of very high performance, 
the methods of calibration should be brought up to the highest possible 
standards. There are indications that the photographic method and the visual 
methods do not give identical results so; it is necessary to clarify the situation 
and if necessary, in the near future, to decide upon the purely photographic 
method as the standard method for camera calibration. The second amendment 
is the use of the point of symmetry. We have calibrated a number of different 
cameras made by different manufacturers from different countries. These results 
show that in a non-perfect lens, in an actual lens, the principal point of auto- 
collimation and the fiducial centre and the point of symmetry do not coincide. 
In the cameras we have tested, the differences between these points are of the 
order of 30, 40 microns and sometimes 0.1 and 0.2 mm. These values cannot 
be neglected because they result in appreciable assymetric distortion. Now it is 
a sound practice of many institutes that they determine the position of this 
point of symmetry, but it is confusing if the resulting point is then called princi 
pal point, as it is sometimes in practice. Therefore I propose to define the »point 
of symmetry» also in this proposal,—the best way is indicated by Roelofs in 
his wellknown paper in »Photogrammetria»,—and then to include this determi 
nation in the draft. This has several important advantages for practical opera 
tions. 
The last amendment is, that there is still a confusing situation regarding the 
definitions which we use. Even the most basic concepts such as principal point, 
principal distance, are not yet internationally standardized. It is not only the 
task of commission I, but also of other commissions to agree and to promote 
international agreements on these basic definitions. This is urgently necessary. 
Conclusions: First of all, the paragraphs relating to the determination of image 
quality should be left as they are. 
It should be clarified whether photographic calibration is necessary and if 
so the photographic method should be explicitly specified, the point of symme 
try definition should be included and its establishment should be specified and 
definitions should be internationally agreed upon. 
Mr. F. L. Corten se declare assez satisfait des essais du projet de norme. Il espère, comme le 
Dr. David, que dans un avenir rapproché on pourra donner une définition plus stricte de la qualité 
de l'image et propose de laisser en l’êtat la question de la résolution pour l’instant. Il trouve