This allows you to select the image area used by the CMOS sensor.
Solution
Selecting the Sensor Mode
This allows you to select the image area used by the CMOS sensor. Based on your selection, available video configuration options will differ. When using the optional MO-4E or MO-4P Mount Adapter, or to shoot in slow & fast motion recording mode using a cropped frame, make sure to select [Super 16mm (Cropped)].
Open the [Sensor Mode] submenu. MENU/EVF [Camera Setup] () [Sensor Mode]
Alternatively, using the HOME screen: HOME [S&F FPS] [OPTIONS] [Sensor Mode].