Thank for all the answers! I don't know how to use the multiquote system yet, so I'll answer as many questions as I can here.
I took at least 50 shots of the rabbits at various settings. They all looked similar - apart from ISO noise. I also moved further away, and tried some more. Some of these turned out much better, but not quite "tack" sharp.
I tried various IS settings. My default is to have both camera and lens set to IS on. Yesterday, I tried some shots with both on, both off, and lens alone, and camera alone. When both were off, you could see the effects of camera shake, as well as the "fuzzy" effect in the image above.
I generally use C1 for ground shots. I only shoot RAW, so I don't bother too much with the JPEG items. WB is set to AUTO, picture mode natural.
Mode = MANUAL
ISO is set to AUTO max 6400.
Focus = Manual ( Pushing AEL button forces an autofocus)
Focus Area = single small spot at centre
Face Detect = OFF
Aperture = F5.6
Shutter = 1/250 ( I change this depending on how bright the day is - 1/640 on bright day)
C2 ( for birds in flight)
As C1 except cluster autofocus in CA (without tracking), and shutter usually 1/800 - 1/2000.
I've also been trying IS off for C2.
I'll post the full image when I get home this evening. However, there isn't an obvious area of focus.
I've done quite a bit of astrophography at focal lengths up to 6400 mm, so I have a good feeling of focus issues and camera stability. For example, if you pass through the point of focus slowly you will get flashes of "clarity" even when handheld. This wasn't happening yesterday. The image looks fuzzy the whole time as I pass through focus.
I'm familiar with camera shake, and this looks quite different. There are no double twigs, or ghost images for example.
I was using the camera handheld, but I can successfully get good images down to 1/25s at 400mm. The image stabilisation on these cameras is really superb.
I'll take a photo pf the SCP as soon as I get home - about 6:30.
I'll also figure out a way of making the raw file available.
The images were taken near Hannington in Berkshire. There are lots of red kites there, and I've found a good spot to park up.