I promised to do this experiment a few days ago so here it is.... This is a birdbath in my yard with a 300mm no name lens but since it is the same base lens that makes no real difference. Shot 1 3oo mm lens. the next image is the same shot with the same lens plus a 2x vivtar extender (doubler) First shot cropped to approx the same size These were with a tripod so there was no apreciable camera shake. In my opinion the 2x seems to have done a little better job. However the image increase was done with a simple editor so not as good as a special fractal program might have done. anyway I promised so here it is.