So far, I'm really happy with the lens. It is light and razor sharp with a quick focus. I'm hand-holding this lens and getting excellent results. Looking forward to using this 800mm lens to catch some amazing bird shots. P.S. It's a great lens for videography too. The nasty bokeh this lens creates when there are bright highlights in the background, such as the shimmering water on a lake or ocean, is its one drawback.

Like most bird photographers, I lust after more reach, less weight, and as low a price as I can get for a high-enough-quality supertelephoto lens. So, with this 800mm lens (even with a Z9 being heavier than a D850) offering a full pound less weight, more reach, and a good (for supertelephoto lenses :-) price, I splurged. Ah, but you pay for those benefits with three other items: #1. this lens does not adjust focus with distance to the bird, especially small erratic ones like swallows, as well as the 500mm f/4 attached (via a 1.4X teleconverter) to my D850; #2 the field of view is narrower; #3 the 800mm does not lock focus on small (as a % of the field of view area) targets as well as the 500mm/TC (effectively a 700mm f/5.6) combo does. The Z9's autofocusing capabilities are superior to the D850 (eye detect and all that wonderful stuff), but that does not compensate for the Z9-800mm combo's lessened ability to catch and hold focus when pushing the edge of the envelope. Swallows go from very difficult subjects to extremely difficult ones, and dragonflies (even more erratic in flight path :-) go from extremely difficult to essentially impossible. Now, maybe younger photographers (I'm 76) have better reflexes, but I'm betting that most of you will find the 800mm more difficult to use than the 500mm/TC combo. You might be better off using the latter with an FTZ converter on your Z8 or Z9. If possible (those 500mm lenses are hard to find, but you may be able to rent one), try both and see what works best for you. Both lenses cost a lot of money ($6500 for the 800mm, $10,800 for the 500mm+TC) and the $4,300 price difference is significant; you should weigh any difference in your keeper rate results with both vs. the extra bucks involved. All that is why I have given this lens 4 stars instead of 5. For the larger and slower-flying birds (herons, gulls, ducks, geese, etc, etc) you will find the 800mm a fantastic 5-star lens to use coupled with the Z9 (and Z8 most likely, but I only own a Z9 so direct experience with the Z8).