0. T. F. and the subjective quality of a large number of photographs as judged 
by a group of observers. An excellent agreement was found, 
The geometric properties of lenses and cameras are rell knov-n in principle, 
With demands for increased accuracy, an understanding of the causes of residual 
errors becomes more interesting. Washer (USA) has studied the effect of lens 
tipping, camera tipping and prism on the radial and tangentral distortion. 
Prism was shown to lead to asymmetry of radial distortion much larger in value 
than the tangentral distortion. Livingstone (USA.) has analysed the measurements 
of 33 cameras and shows that the thin prism analogy only holds for angles less 
than 21 from the axis. 
Brown (USA) however has done an exact ray tracing through a prism and 
finds agreement 7/ith Livingstone's measured results. 
Seth (G-erman Democratic Republic) has investigated the effects of 
temperature gradients on the geometric properties. 
Another problem of film cameras is the flatness of the film at moment of 
exposure. There is some evidence from Sweden that polyester film is particularly 
difficult to keep flat, but I do not know whether this is the general experience. 
The geometric properties of the film itself, and the diapositives or 
contact prints made from it, have been studied by many research workers, too 
many to mention here. Slowly we are learning how to expose, develop and copy 
from film to leave negligible residual distortions. 
10. Future Work of the Commission 
Experience has shown that the results from the Working G-roups has been 
disappointingly small. Reasons are not hard to find. 
(a) The Working G-roups took some time to set up after Lisbon Terms 
of Reference had to be written and agreed, Chairmen had to be invited and 
members sought from the National Societies. 
(b) The business of the Working Groups has to be carried out by 
correspondence, always a slow matter. Frequent meetings of the 17. G. are 
desirable but travel is expensive in time and money, and it is very difficult 
to find a date when every member can be present, 
(c) The Working Group finds it difficult to have a research task carried 
out, unless it happens to be consistent with a member's normal employment and he 
can obtain authority to undertake it. 
(d) The Working Group has no finance allocated to it, even for printing 
of reports and postage. 
It is clearly too soon to make a final judgment on the value or otherwise 
of W.G. *s. Certainly there has been some valuable work done by them and they 
have made the job of organising the Commission's programme easier for Lausanne 
than for Lisbon. 
/Perhaps