The first Corona satellites had a single camera, but a two-camera system was quickly implemented. The front camera was tilted 15° aft, and the rear camera tilted 15° forward, so that a stereoscopic image could be obtained. Later in the program, the satellite employed three cameras. The third camera was employed to take "index" photographs of the objects being stereographically filmed. The J-3 camera system, first deployed in 1967, placed the camera in a drum. This "rotator camera" (or drum) moved back and forth, eliminating the need to move the camera itself on a reciprocating mechanism. The drum permitted the use of up to two filters and as many as four different exposure slits, greatly improving the variability of images that Corona could take. The first cameras could resolve images on the ground down to in diameter. Improvements in the imaging system were rapid, and the KH-3 missions could see objects in diameter. Later missions would be able to resolve objects just in diameter. A single mission was completed with a resolution but the limited field of view was determined to be detrimental to the mission. resolution was found to be the optimum resolution for quality of image and field of view.