NASA Photograph
This photo of the Earth was taken by the first Lunar Reconnaissance Orbiter in orbit around the Moon. It was taken using the 75mm (wide angle) lens of the Lunar Orbiter camera. The sprocket holes along the lower edge are visible; similar sprocket holes at the top are lost in the general black background of space. The sprocket holes are nesessary for positioning the film during exposure, developmen, and scanning. A given image is exposed and developed once, but may be moved back and forh several times during readout
Readout is accomplished by moving the film in tenth-inch steps through the scanning station. A 5-micron spot of light sweeps back and forth across the width of the strip. Following each horizontal sweep the spot is moved vertically slightly less that its diameter. It takes about 17,000 sweeps to cover each strip. The movement is rebversed on completion of each sweep and each sytip
On the ground, the signal is recorded on magnetic tape. The tape is played back through a kinescope, turning the electrical signal back into variations in he brightness of a light. The light is recorded on 35mm film, reversing the readout performed in the satellite.
The visible defects in this image were introduced in the ground reconstruction process. Applying modern digital photographic techniques with much more powerful computers, high-quality images have been produced from the original tapes.