Nikon has just announced their latest telephoto prime. It's not the PF (DO) technology but standard design. At f/4.5 it's 2/3rd stop faster than f/5.6, a 1/3rd stop slower than the Canon 400mm f/4 DO II at about half the price in the UK, £3.300. It's light at only 1.245 kg. The price is the same as their 500mm f/5.6 PF, but the MTFs are not as good. Some will like it as a light walk-around telephoto lens. For me, the modern zooms are sharp enough and so much more versatile. Despite that, the f/4.5 aperture would get more detail out of the R7 sensor and I would like to see Canon have something similar on offer, and would even consider one to pair with it for serious birding trips.