
a piece of temporary solution :
you have to deconnect maya camera aperture and maxwell camera,
create an expression between filmwidth and height and horizontal and vertical aperture.
Then when you change filmwidth and height in mxw cam, it changes the viewport in maya.
It works approximately with normal range of focal length, it's a little wrong with extrem ! But it gives a good idea of the final result.
(you have to make sure that your maya res and aspect ratio)
the script :
CBdeleteConnection "Maxwell_CameraShape.hfa";
CBdeleteConnection "Maxwell_CameraShape.vfa";
expression -s "Maxwell_CameraShape.horizontalFilmAperture = MXCamera1.filmWidth * 0.039;\r\nMaxwell_CameraShape.verticalFilmAperture = MXCamera1.filmHeight* 0.039;" -o Maxwell_CameraShape -ae 1 -uc all ;