I agree, the auto focus will have trouble targeting the planet so it will end up unfocused. Manual focus under the macro control will help but still might now be enough. Try using a cheap telescope with an point n shoot telescope mount. It will usually be an adjustable mount with a platform to secure the camera with with knobs to adjust it's position in the xy axis. The telescope is held by an eye piece clamp and a tripod mount on the bottom. These can be used with any optical sight, rifle scopes, telescope, microscope, binoculars, monoculars, anything pretty much. I suggest a basic short telescope, I sometimes use a 45x90mm 18+- inch tasco telescope but any will do. Good luck.
