The four types of cameras on board the Mars Exploration Rovers are called the Panoramic Camera (PanCam), the Navigation Camera (NavCam), the Hazard Avoidance Camera (HazCam), and the Microscopic Imager (for close-up views).  The lenses for these cameras have to be small, simple, and effective, and they must survive getting to Mars and on Mars.  The most has to be done with the least.  Thus the least number of lens elements are used.  Only two types of optical glass (one crown and one flint) are used throughout (with one exception).  All optical surfaces are spherical or flat (no aspheres).  And no cemented surfaces are allowed (that could break apart in the Martian cold).  There can be no mechanical shutters, variable aperture stops, or refocusing that could malfunction.  Short focal lengths (to match the CCD format), small apertures (to allow great depth of field), and electronic shutters (frame-transfer CCDs) make these restrictions realistic.  To facilitate polishing, anti-reflection coating, and mechanical mounting, the lens elements have been made somewhat oversized.  In no case is any mechanical vignetting (off-axis beam clipping) allowed.

A temperature of 23°C and an air pressure of 0.95 atmosphere were adopted during the optical design process on the assumption that these lenses have to be made, tested, and calibrated here on Earth.  However, image quality was reevaluated analytically for the Martian environment of 10°C, -22.5°C, and -55°C, all at 0.01 atmosphere.  In no case was a significant change found when going to Mars.  Nighttime temperatures on Mars can fall to -120°C, but the cameras need only survive, not operate, in those conditions.

All the cameras use the same type of solid-state, silicon-based CCD image sensor and associated electronics.  This flat CCD is a 1024 x 2048 array of 12 x 12 µm pixels.  It is a frame-transfer type, as described earlier in Section A3.2.  The top 1024 x 1024 pixels is the photo-sensitive area, and the bottom 1024 x 1024 pixels is a covered frame-transfer buffer.  Thus the active imaging area is 12.29 mm square with a diagonal of 17.38 mm.  (Relatively speaking, in photography this is not very small.  The diagonal of a 16 mm movie camera frame is 12.63 mm, and the original 8 mm movie frame had a diagonal of only 5.95 mm.)  The CCDs themselves are sensitive to wavelengths ranging from about 0.40 µm to 1.1 µm.  Filters plus the CCD response determine the specific wavebands.