The specs on the Fujinon CM-W series are available here.
Originally Posted by kapitman
The 450mm CM-W takes 86mm filters. Not really all that big for a lens this long. It's the same size filters as a 240mm APO Sironar-S and smaller than most 300mm and 360mm plasmats and most modern 8x10 wide angles.
It's well documented that the 450mm Nikkor M covers a LOT more than the published specs. I'm using one on 14x17 and have plenty of coverage. I don't have anything bigger to try it on, but the image circle needed for 12x20 isn't much bigger than for 14x17. I believe if you search the archives here and on the large format forum you'll find testimonials from several photographers who have successfully used the 450mm Nikkor M on 12x20.
Really Big Cameras