Chris Malcolm wrote:
I'm playing around with shooting birds in flight with the 500m reflex. It has such a narrow field of view on a crop sensor DSLR that it's extremely difficult to successfully point it at a flying bird in the first place. But when I do succeed in getting the bird in the middle of the frame, the AF will slam the bird into focus and take a shot. If I was lucky enough to have the AF point on the bird's head of course. Given the great difficulty of aiming such a long lens at a fast moving bird I'm more likely to have focused on its tail or the end of wing as the bird's head. But maybe that's because with only the central AF sensor it doesn't do focus tracking and the bird flew out of focus in the AF/shoot lag time?
500mm (effective 750mm on your A550) is quite long to try to take BIF photos so I can imagine how difficult it is. I remember that back in film days a lot of people were using the Canon 400mm f5.6 for those photos. I think in those days Nikon didn't have one and Moose Peterson wrote an article about how much he liked using the Tokina 400mm f5.6 on his Nikon for BIF photos. 400mm vs. 750mm would make it easier to track birds, although they would, of course, be smaller. With your A550 that would be more like a 300mm lens. Anyway, I don't really take these kinds of photos so this is not advice, just passing on what I read about 15 years ago.