I have the Komura in several mounts and the Vivitar 2X Macro in a number of mounts too. You may find that using a 2X teleconverter of any kind on a 200/4 lens to be a frustrating experience. Even with a Nikon F2 or F3 with a plain matte or grid screen, focusing is difficult. Putting the camera on a tripod can help but only if your subject is not moving. Just about any 300mm Nikkor after the f/4.5 P will give you better results, even after cropping. I have not tried either of my 180/2.8 Nikkors with telecoverters but I have had some luck using 1 200/2.8 Canon New FD (1st version) with a 2X teleconverter in good light and on a Canon F-1 with an L D screen. I used both the Vivitar 2X Macro and a Canon FD 2X-A. When would I use a 200/4 Nikkor 'K' or AI with a 2X teleconverter? Maybe for some macro shooting where I can't get s close to the subject as I would like.