He was a Magnum photographer and the main moto then was "F8 and be there". aka zone focusing, using DOF scales printed on the lens. Also, the max aperture was not as wide as what we have to day. F2.8 was often already considered to be a fast lens for 35mm or 90mm focals.
Plus there were good focusing helps, like the split screens in the non reflex VF : you just picked a line from your subject and when the two halves of the line became aligned, you were in focus.