Sharp Photos - Where am I going wrong?

[markgriff]

Help! Where am I going wrong when it comes to getting sharp photos?

I saw the fox below in the field at the back of my place today and took a few shots. However, every single one came out similar to the one below - lacking in sharpness with the subject out of focus!

I had the camera set up on a sturdy tripod with a cable release attached to avoid camera shake. I chose an apeture of f5.6 and ensured that the seleceted focus point was over the fox's face in an attempt to make sure that the eyes were sharp. Despite this, I ended up with the usual disappointing results??

I was using a Canon 20D with a Sigma 100-300mm f4 lens and a Sigma 1.4 converter attached.

Any help would be much appreciated!

Thanks,