I'm not clear on which Arri Alexa model you have. We have settings for the EV, EV Plus, and OV. Is yours one of those, or some new kind that we don't know about yet?
If your camera is basically an EV or EV Plus, but with a mask to change the aspect ratio, then here's what you'd do:
- Open the "Set Film/Video Frame Size" dialog.
- Click the "Create New Size" button.
- Set the film size pop-up to High Definition Video.
- Assign it some aperture name of your choice.
- Set the aspect ratio to 2.35.
- Set the film width to 23.79 (same as what we show for EV and EV-Plus).
- Click OK to close the second dialog and save the new format.
- Select the new size in the first dialog and click OK.