A lens which would be very hard to carry, and nearly impossible to shoot with. Not to mention shooting *hand-held". Which is just what I did here! (Above 300mm was considered impossible by most.)
And I did it in dark weather, pretty close to sunset. And basically ALL the pictures were sharp. One image of these two is a crop of "100%" of the other one, meaning all you can get out of a picture. The is the longest lens I've had, in performance speaking (tele-reach).
...In physical size, somewhere I have an old manual-focus bird-photographer's 500mm lens. This lens was not sharp, it did not zoom, focusing with it was hit-and-miss at best, and it was so big you were likely to be taken down be the police by your third photo. (No joke, I'd hate to walk around in people'd areas with that thing. (In contrast this lens is half the size/weight.))
Auto-focus and auto-stabilisation has a *lot* of the honor of the performance of these lenses. High-sensitivity digitial sensors a lot of the rest. My raw talent has... well, not a lot. :-)
[For those who wonder about the un-sharpness of parts of the picture (forground/background), this depends on the settting of the lens' "aperture" and can be used creatively. It's a natural optical phenomenon.]