Playing with a new toy. I recently purchase a used 2xiii canon tele-extender for my 500mm f4L lens. With the extender the 500mm becomes a 1,000mm lens, although instead of f4 it becomes an f8 (loss of 2 stops). This new series III extender is much improved over previous versions. Although there is a small amount loss of sharpness, its really acceptable to me, given the extra reach. This is essentially a full frame image. It was cropped only to fit onto the web site page.