>Yes, the Nikon 200-400 uses regular 52mm filters as long as >they are not too thick. I use the B&W 3.0 (10 stop) ND >filter to take photos of the sun. Live view and eyepiece >closure are advised to save your eyes from UV and IF light >than may or may not be coming through the lens even with the >filter.
You don't worry about overheating internally? From my telescope days, I never used anything but a front objective filter, like Thousand Oaks.