When you turn the focusing ring of a Canon EF mount lens, the viewfinder automatically enlarges for ease of manual focusing.
This feature requires the AF/MF switch of the Canon EF mount lens to be set to the MF position and also requires a Canon EF mount lens that supports distance information. Virtually all Canon lenses introduced in the last 20 years support distance information, but a number of notable lenses, such as EF 35/2, EF 50/1.0L and EF 50/1.4, do NOT support distance information and do NOT support auto-magnify MF assist on a Sony NEX camera body.
Auto-Magnify MF Assist is disabled when the Smart Adapter is in Green Mode.
NEX camera bodies in camcorder form factor do NOT support Auto-Magnify MF Assist.
MF Assist can still be actuated manually when using lenses with no distance information support or when the Smart Adapter is in Green mode, or on a NEX camera body in camcorder form factor. Consult your camera body's owner manual for details.