I always like to carry a Nikon or Canon 400mm 2.8 for zoo trips but the weight was a issue to handhold so thought about it had an idea . I have a Nikon 300mm 2.8 AF-s , bought another Nikon 300mm 2.8 VR , plan was to sell the 300 AF-s (prices have dropped ), then had an idea to keep the VR by itself and add on the 300 AF-s a 1.4 or 2X extender, that way I can switch the lenses , Any comments ?