I was wondering if my Sigma 2x converter would work with the Canon 100-400 IS and what do you know, it does. Here is a full frame shot I took earlier of the moon. A bigger version and a crop can be seen on Flickr. Clicking on the pic will bring you there.
I find this image very sharp.not at all soft, I tried the 100-400IS plus the 1.4X II converter and have softer than yours.Does your auto focus not work with this combination?? I know the Canon 1.4X and 100-400 does not.Unless its f2.8
The auto focus doesn’t work with it but I tend to manual focus with the lens anyway. The IS does work though :) I must admit that there is a little USM used. Thanks for looking.