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water jackets for temperature control, increase in the size of washing tanks to 
obtain hypo elimination to archival standards, the use of an air blast squeegee 
to remove surplus water from both sides of the film, and an extensively rebuilt 
Lau blower A-10 roll film dryer. Temperature of the drying air is between 90° 
and 100°F. Both continuous processing installations use a solution temperature 
of 68°F +1° and are monitored by routine sensitometric control. Two other 
types of film processing equipment are in extensive use. The Morse type B5 
motor-driven developing units are used with a solution temperature of 68°F 
± 1° followed by the A-10 film dryer. A gamma of 1 - 0 is normal for this equip 
ment as determined by sensitometric control used infrequently as spot checks. 
For the relatively small film from the Eagle V cameras RAF spiral processing 
equipment is used with solution temperatures between 68 and 70°F for a gamma 
of about 0-9. For drying the Fairchild-Smith film dryer is used without heat 
but preceded by a wetting agent. The developer in this process is Kodak D76. 
Reconditioning of film to equilibrium with the relative humidity at which 
it was exposed is carried out by one organization, the Photographic Survey 
Corporation, before making diapositives. This procedure ties in with that 
company’s development and use of a camera magazine having humidity control. 
Unexposed film is stored at temperatures ranging from 50°F to 68°F. 
The ambient humidity is also controlled in some cases. However, it has been 
shown that the metal tins sealed with tape in which the film is supplied are 
sufficiently good vapour barriers to ensure that the film will not change appre 
ciably from its spooling humidity for several years, hence the equilibrium 
humidity is between 55 and 60%. Various storage conditions apply after pro 
cessing. Those for which data are available are as follows: 65°F to 80°F with a 
relative humidity from 35 to 60%; 60°F with relative humidity from 40 to 50%; 
and 60°F with 60% relative humidity. 
For the ground photographs which are taken with the theodolite camera, 
the sensitive material used is Ilford extra-fine grain infrared sensitive plate. 
England 
The most commonly used film is Kodak Super XX topographic base. This 
film resolves 30 lines per mm for a target contrast of 2:1. Speed is tested by the 
Directorate of Colonial Surveys in an intensity scale sensitometer with an 
exposure time of 1/30 of a second. A minus blue filter is used. Development 
is in Kodak D19. 
A recent investigation of film distortion by the Ordnance Survey Office 
was carried out with an F49 camera carrying on the register glass a fine reseau 
of crosses. It demonstrated that differential film distortion may easily occur in 
such a way that when corrections deduced from measurements made between 
collimating marks are made to points in the corners of films, these points may 
still be in error by amounts up to 0 -1 mm due to the irregular nature of the dis 
tortion. For the two cases investigated there was no evidence of local emulsion 
slip calculated to cause errors greater than 0-01 mm. 
Various processing procedures are used. Government organizations use a 
continuous processing machine with solution temperatures of 70 to 75°F to 
produce gammas between 1 -3 and 1 -8. One private firm uses Morse processing