I experimented a bit today. I use a Canon 100mm macro to shoot insects but I find I often can't get close enough to some of the smaller gnats and leafhoppers and things like that. I purchased a 12mm extension tube and I already had a 1.4x TC so I took some comparison shots of the various setups, here are the results for those that are interested.
The first one is the 100mm macro only. Each of these photos are focused as close as they can be.
http://img.photobucket.com/albums/v1...uk/macro01.jpg
The second is the 100mm macro PLUS 12mm extension tube
http://img.photobucket.com/albums/v1...uk/macro02.jpg
This final image is taken with 12mm extension tube PLUS 1.4xTC.
http://img.photobucket.com/albums/v1...uk/macro03.jpg
This gave me the closest focus by far. These results are pretty much as I expected them to be but it is nice to see te results isde by side.
Cheers,
Russ