For the EOS 5D MkIII We have found that the EF 40 mm 2.8 STM firmware update failure with the EOS 5D Mark III can occur if the camera has Battery Info Registered and if the Battery Info is checked right before the firmware update is applied. To restart the firmware update please follow the below procedure.
The Variable Aperture AE control will not operate, but you can manually adjust the aperture ring of the lens. A basic exposure guide to follow for bright sunlight (with distinct shadows) is to make a fraction representing the shutter speed needed at f / 16 by putting a "one" over the film's ASA rating. With a film of ASA 100, use 1/100 sec.