Located next to the PanCams in the turret on top of the mast is a stereo pair of moderately wide-angle NavCams.  These are engineering cameras intended primarily to help direct the rover as it drives across the Martian surface.  Nevertheless, they have been giving much science data too.

The NavCams point in the same direction as the PanCams and have a stereo separation of 200 mm.  Lens focal length is 14.67 mm giving a field of view of 45 x 45 degrees, or 60.7 degrees on the diagonal (the equivalent of a 37 mm lens on a 35 mm camera).  They operate at f/12, view objects whose distances range from infinity to 500 mm, and are fixed-focused at 1000 mm.  They are monochrome (black-and-white) systems; a pair of absorption filters (Schott OG590 and KG5) working in series gives a reddish waveband extending from roughly 0.60 µm to 0.80 µm.  This matches the predominant color of the Red Planet (although, technically speaking, the color is a light-to-moderate yellowish-brown).

The lens design is a cross between a Hologon and a Biogon and is shown in the layout in Figure 31.2(a).  A true Hologon with a deep groove around the center element was rejected for this application because the narrow waist might break apart during the vibrations of launch and shocks of landing.  For safety, the center element was divided, and a conventional fixed aperture stop was placed between the two halves.

Figure 31.2(b) is the polychromatic spot diagram.  The scale bar length is again 24 µm.  The circles indicate the diameter of the Airy diffraction disk for a wavelength of 0.70 µm.  On-axis, the main aberration is primary longitudinal color.  There are virtually no additional aberrations off-axis.  Color is not corrected because the lens has insufficient degrees of freedom.  To do so would require more elements (some typically cemented together) in the center group.  But that is not allowed here.  It is also unnecessary because image quality is already easily diffraction limited, given the slow f-number and short focal length.  Distortion is less than 0.03%.  Image illumination at the edge of the field is 63% of the central value.