1. A wafer-level array camera, comprising: an image sensor wafer including a M×N image sensor array, M and N are positive integers; a spacer disposed on the image sensor wafer; and a lens wafer disposed on the spacer, the lens wafer including a M×N lens array, each lens of the lens wafer having the same back focal length and being disposed at the same distance from a respective image sensor of the image sensor wafer.