This figure is a ray-tracing diagram from the optical design of the MDIS Narrow Angle Camera (NAC). The NAC has a 1.5° field of view, a focal length of 550 mm, and a 24-mm aperture (resulting in an f/22 system). It uses an off-axis Ritchey-Chretien design. The ellipsoidal primary mirror and hyperboloidal secondary mirrors are gold-coated aluminum. A bandpass filter is the first optical component of the assembly. This filter defines the spectral range of the instrument. A specially designed interference coating serves as a heat-rejection filter, preventing the substantial infrared radiation emitted by the surface of Mercury from entering the instrument and heating the detector (CCD).
Date acquired: April 23, 2013Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington