I don't do reviews

as such -- I bought a Canon 5D4 just before going to Canada and used it for all my bird photos and some landscapes with the 400DO2 and mainly 1.4 converter while there -- the high ISO performance was much appreciated in the generally cloudy conditions that typically necessitated 1600ISO and up to 4000ISO but what struck me most and it was apparent with the Pallid Harrier was the autofocus accuracy on small subjects even at long range and also the amount of detail that it is possible to see in very small images -- here are some stupidly large crops of some seabirds taken from the shore by the cottage -- with 10x32 bins I could not actually see what they were -- the second image shows the specks in the frame, birds to the right are Surf Scoters, and the admittedly terrible lower images show the extent of the crop and how they can be seen to be Marbled Murrelets -the larger image is full frame cropped to 1600 pixels wide--- this is probably not the greatest example but other will follow -- also attached a flock of Red-necked Phalaropes taken from the back of a bouncing, very speedy boat as the birds flew past at speed --