a4 AF-on versus shutter/AF-on
When I select a4 AF-ON only mode in d800, I am not getting focus responses after using the camera for just a little bit. That is, the lens and image will not change focus after pressing AF-ON couple times. Switching back to Shutter/AF-ON makes it responsive again. What is happening here? Is my AF-ON defective? This is happening to both 50mm 1.8g and 70-210mm af-D lenses.