Question: question about legacy lens

C-mount works just like any other adapted manual lens. The NEX cameras don't have a metering issue with any lens, but you do have to set the camera to enable release without lens.

Note that C-mount lenses are generally intended for MUCH SMALLER sensors. Thus, some vignette so severely that you might get "bad" exposures from averaging over too large an area of the APS-C frame. Setting the metering mode to center/spot will take care of that.