On the Library of Congress’s Worlds Revealed blog, a fascinating piece on a fascinating piece of hardware used by NASA to process lunar photographs taken for and by the Apollo program into orthorectified imagery useful for mapping.

Designing these photography systems was quite complex, as the team had to account for the movement of the spacecraft, distortion introduced by the camera’s lenses, variation in terrain on the lunar surface, the scanning speed of the camera, the angle of the sun at a given time (which affected the amount of light available), and extreme temperature changes (to name a few!). Apollo’s new panoramic camera produced film images with very wide angles, resulting in a distortion of scale and a curved horizon with a varying scale. […]

To make the panoramic photos useful for mapping, the images themselves needed to be corrected such that the distortions introduced by the spacecraft motion disappeared. Enter the Apollo Transforming Printer. It was able to remove the distortion introduced by the panoramic camera by reconstructing the motions of the orbital camera. Unlike today’s digital rectification processes, this was an optical remapping. The Printer utilized the original film negative, reprojected it through a lens and mirror system, and produced a print that was geometrically corrected.