I was chatting with Warren and was complaining about focusing on birds when they are flying right at me, and it came to me, a way to try to over come it. In this situation, with my camera set (a1 and a2) to shoot only when the image is IN FOCUS very often the camera won't take the photo(s), and frustration ensues. In the past I've tried to use the focus lock (/exposure lock) button, but with a subject getting closer the focus goes off almost right away ( it is way easier when a bird is just flying by you, not at you!!!). Anyway, I realized using the 200-400mm's manual focus over-ride was the way to go. I tried it a few times, and it worked! It will take some learning and etc, and lots of not perfect images, but it will work. If the subject is getting closer then the focus ring has to be turned counter-clockwise.
I've had the Nikon 200-400mm f/4 lens now for about 9 months and had never tried the manual focus over-ride feature on a moving bird. The way I thought about it was that a nearly 2 thousand dollar camera (D300) and a 5 thousand dollar lens (at f/4) should be able to get good focus on just about anything. So I never tried it.
A handful of times I would try to use the focus lock button to let the camera shoot but as you can see from these 2 examples below it wasn't even worth it.
Early on when I got my D200 and again with my D300 I changed the default setting for focus behavior so that it requires focus to let me take the shot. On the D300 this is setting A1 and A2. They call the settings Release Priority and Focus Priority. With release priority it will start taking shots right away and work on adjusting focus too, but won't restrict shooting. In Focus Priority the camera requires gaining focus BEFORE the camera will take the shot.
Normally when a bird is flying by the camera can do a good job on focusing and shooting. The worst is when the bird is flying right at the camera. The camera wants to get the image in focus and will be constantly readjusting focus, and thus very often never shooting an image.
I've tried a number of different focus settings, like single sensor (the center one) and center plus group assist (D300 middle setting for rear focus selector), and always AF-C (continuous focus mode) for moving subjects.
So I tried this new way to shoot. I'd use the autofocus of the camera and then when it got close to right I'd start adjusting the focus manually. I've seen the above bird behavior before but I don't think I ever got a decent shot of it. The bird is approaching its nest, and tucked in its wings a bit, accelerating, and flying somewhat towards the camera. I'm pretty happy with the results of just an hour trying this new way to shoot.
I think this is the best example I have from last weekend of the technique and resulting images. Here's a small sized version without any cropping:
And here's a 100% crop of the center without processing as well:
This is the final version, cropped and processed fully (levels, shadow recovery, sharpening, etc):