With 200m at f/2, choosing exactly where you want to focus is critical. While relying on autofocus to choose can sometimes work, it often might choose something just in front of or behind you desired subject.
Consider the scene below with the subject about 200 feet (61 meters) distant. Tree branches are about as non-planar as one can get so where to focus depends a lot on what is intended.
Article continues for subscribers...
diglloyd Advanced Photography includes hundreds of pages of exclusive coverage and high resolution, Retina-grade example pictures detailing Canon and Nikon DSLR bodies and their lenses, with in-depth analysis of sharpness and contrast, color, bokeh, vignetting, distortion, MTF, and flare. Also included is a wealth of in-context technique and workflow insight. Since 2006, diglloyd Advanced Photography is the authoritative review and on-line reference for discerning Canon and Nikon shooters. Subscriptions cost $ per year.