I was shown one of these by John Brewer at his WP workshop. Great idea and I just had to get one. It took a while of searching on the internet and good old Fleabay to find one. I managed to get this one boxed with paperwork from the US.
The aperture can be set from 3/4″ to 3 3/4″.
I can now fit all but one of my lenses onto my different sized cameras.