MISR employs nine discrete cameras pointed at fixed angles. MISR's cameras are named Df, Cf, Bf, Af, An, Aa, Ba, Ca, and, Da, beginning with the most forward-viewing oblique camera and ending with the most aft-viewing oblique camera. The initial letter (A, B, C, D) denotes the focal length of the camera lens, with the A cameras having the shortest focal length and the D cameras the longest. With the exception of the A design, which is used for the nadir view as well as the near-nadir views, each letter (B, C, D) also denotes the camera angle, that is, the zenith angle of the optical axis of the camera. The small letters (f, n, a) denote whether the camera is looking forward, nadir, or aftward. Nominally, the view angles for the off-nadir A, B, C, and D cameras are 26.1, 45.6, 60.0, and 70.5 degrees, respectively, relative to a local horizontal plane at mean sea level. There may be small variations with orbital position and location within the field of view. In the product file names, both letters of the camera name are capitalized.