294 Mastcam, shown in situ in Figure 1, consists of two camera heads mounted on the rover's Remote  Sensing Mast (RSM), along with paired digital electronics assemblies located inside of the rover. The Mastcam camera pair, providing a humanlike perspective 2 meters above ground level, will serve as the "eyes" of Curiosity, in a similar fashion to that of the Panoramic Cameras (Pancam) on the Mars Exploration Rovers (MER), Spirit and Opportunity. These cameras will provide color images and high-definition video of the rover's surroundings, gather information about nearby terrain, and assist driving, navigation and sampling operations. Images can be combined for panoramic views and 3-D effects. Each Mastcam camera head is equipped with 8 different optical filters, changed via a filter wheel mechanism, providing a total of 13 unique filter options. The Principal Investigator of this instrument is Dr. Michael C. Malin of Malin Space Science Systems (MSSS).   Some of the new features that the Mastcam system will bring to Mars 2,3,4 are:   Active focus capability: A lens group is mechanically actuated for focus between 2 m and infinity.   Differing Effective Focal Length (EFL) lenses: One camera head features a 34 mm focal length,  f/8 lens while the other features a 100 mm focal length, f/10 lens. The 34 mm EFL lens provides a wide field of view: a 15° square field of view obtains 450 μm per pixel images at 2 m distance and  22 cm per pixel at 1 km distance. The 100 mm EFL lens enables detailed images of distant objects: the 5.1° square field of view takes images with a scale of ~150 μm per pixel at 2 m  distance and 7.4 cm per pixel at 1 km distance.    A Bayer pattern filtered CCD detector, providing natural color (i.e., what the human eye would  see) pictures and video of Mars.   Ability to take 720p high-definition video (1280 by 720 pixels) at approximately 7 frames/second.  Electronics within each camera head can process data independently of the rover's central  processing unit and can store thousands of images or several hours of high-definition video with 8 GB of internal memory. Thumbnails can be sent to Earth for the science team to review before full resolution images are transmitted (or discarded). The camera head electronics can analyze images for best focus and also combine in-focus portions of multiple exposures for greater depth of field images in a process called focus stacking or z-stacking. The electronics can be updated with new software when desired.   Variable focal length, though originally planned 5, will not be part of Mastcam's capabilities. Variable focal  length, "16x zoom" lenses (the subject of this paper) were designed, and later built, for Mastcam to provide a wide range of imaging and video capabilities. The 16:1 zoom lenses allow for wide field of view images at 6.2 mm EFL (f/6.2), telephoto close-ups at 100.4 mm EFL (f/10.5), and any EFL between these extents, all with the same lens. Zoom lenses would have also enabled stereo (3-D) video recording and quicker acquisition of stereo images.  

Figure 2: Mastcam Zoom Lens  Assemblies

In 2007, late in the design phase, the zoom capability was removed from the Mastcam lens by MSL  project management for risk and cost reduction purposes. The project redirected the team to design and