Lunar Orbiter

Before they could land on the moon, NASA needed to photograph potential landing sites. To do this, they built the Lunar Orbiter. Five of these were flown between 1966 and 1967. Together, they identified twenty landing sites and mapped 99% of the moon's surface. The camera system had a particularly interesting history. It was first designed for the SAMOS spy satellites. It was a technical marvel: it was an analog machine, but could transmit near-real time photography. It could also automatically compensate for the speed of the satellite. The camera system was still highly classified, so NASA couldn't reveal too many of the details of how it worked. This NRO article talks about the technology transfer as well as the camera's technical details: https://www.nro.gov/Portals/65/documents/history/csnr/programs/docs/prog-hist-01.pdf