this then gives 35mm full frame reach equivalence of a 1200mm lens with cropped aperture of f/8 which is not possible to achieve by any other mechanism at this image quality, low weight and low size (of course it cannot compete with a full frame 600mm f/4 lens with 2x TC in terms of image quality, shallow
depth of field (DOF) and high ISO performance, but then such a full frame lens is far heavier, larger and far more expensive and you wont get it into cabin luggage on your flight)