Wide-Open/Custom Function Button
Assignable Custom Function Button
On A7 series and A6300, the button on the adapter serves as the assignable "Focus hold" button found on Sony G series lenses. You may for example assign "Aperture Preview" to the the "Focus Hold" button on an A7 series camera or A6300 and get the same DOF preview function as on a Canon DSLR. This assignable button function is available only on A7 series and A6300. Consult your camera's owner's manual.
On cameras other than A7 series or A6300, when the adapter is in Advanced mode, or the camera body is in Movie mode, the lens' aperture is set to wide open for ease of focusing while the Wide-Open (WO) button of the Metabones Speed Booster / Smart Adapter is depressed. Release the button and the lens will return to the aperture set on the camera.
This wide-open function is automatically shut off when you actually take a picture and during movie capture.
On some camera bodies, this wide-open function is unavailable when the Metabones Smart Adapter is in Green Mode.