True electronic integration of aperture diaphragm - let camera automatically choose aperture in P or S exposure modes, or dial in yourself on the camera body in A or M modes. Powered by camera body. No external power source required. Wide open button (opposite of depth-of-field preview function) makes manual focusing easy. The tripod foot is detachable and compatible with Arca Swiss, Markins, Photo cam ball heads. High performance 32-bit processor and efficient switched-mode power supply.
Enhancement on MARK IV vs. MARK III: The new design of inner housing in MARK IV has a bigger inner hole. Improving the Tilt shift lens preformance. The inner hole is painted with matt coating. This can further reduce the internal reflection.