Optics for Mars

JPL's new rover "Curiosity" is en route to Mars, set to arrive in August 2012. A recent NASA press release describes an interesting aspect of the optical sensors carried on board the rover. A special test chart is installed to allow for calibration of camera systems for resolution and color. The chart includes a 1909 Lincoln penny (hey, it's Lincoln's birthday today!) as a familiar size and detail reference, more for public engagement than for any specific science or engineering need.If you zoom in on the above image, you can see that the black & white test chart resolution samples are labeled in cycles per millimeter, the typical unit used by optical engineers to define image quality. A "cycle" is a pair of black and white lines (cycling from white or bright to black), so 2.0 cycles/mm means that two black/white pairs will fit into a millimeter of width (so each bar will be 0.25 mm wide). Higher cycles/mm correspond to finer detail in the image (smaller pixels in a digital image). This chart will be used to calibrate the instrument called MAHLI (Mars Hand Lens Imager) that will provide close-up images of mineral and soil samples.