Determining flexure of aerial camera smoothing glass

Topographic aerial cameras are now in use in which the film is smoothed by being pressed against a smoothing glass on which a grid of fiducial marks is plotted. A significant pressure must be applied for good smoothing. Tests have shown that a pressure of 1.0 to 1.2 x 10 to the 4 Pa is adequate for ensuring a minimum gap between the film and the smoothing glass. The pressure required for smoothing the film causes elastic deformations (flexure) of the smoothing glass and connected parts of the aerial camera. Glass flexure must be taken into account during camera calibration in order to ascertain what photograph distortions could be a result of this bending.