I'm starting doing anamorphic photography and EOSHD has been great helping me understanding this technic.
I'm shooting with a Nikon Df that have a 3:2 ratio. My anamorphic adapter is a Kowa Prominar 16-H 2x.
To find the aspect ratio, I took a photo at home to a circular box and squeezed the image until it turned circular. It gave me a ratio of 2,82:1, as you can see in this image https://www.dropbox.com/s/bmq13xv97syuzx5/DSC_7602_2%2C82.jpg?dl=0
I read an article somewhere that talked about a value of 2,66:1. I tried that but the box resulted a little ovalized https://www.dropbox.com/s/qx