what is the difference between canon 5d mark iii and iv?
The 5D Mark III had a single Digic 5+ processor. ... The 5D Mark IV has two separate processors, a Digic 6 and a Digic 6+. The two processors work at different tasks, the Digic 6+ for image capture, and Digic 6 for metering. Those two processors should make for a faster and more reliable overall operation.