Sorry if this is a bit off topic, but since we're talking about extenders and extension tubes already I don't see the need to start another thread.
If I use a 2x extender and then a 12mm extension tube...is it possible to use the 100 f/2.8L with this combination?
Yeah, I think I've done that. The 12mm extension tube should make the 2x extender fit any lens (although I'd be careful with ones like the 85L which has a very exposed rear element). With a macro lens like the 100L you'll get a pretty good setup for smaller insect subjects, although I'd stop down and you'll lose infinity focus as always with the extension tubes.
Thanks! I just tried it... Man, unless the camera is on a tripod it's next to impossible to hold it steady. Sharpness really suffers, even when stopped down to f/8.
The lens retained it's f/2.8 aperture, however, which was cool!
Thanks again for the information.
Well remember, the reported aperture won't take account of the extender, since the camera body won't know it's there. So "f/2.8" is actually f/5.6. Also, at that magnification (up to 2x), use of a flash is almost essential. Add a flash, set it to the sync speed (e.g. 1/200), and you can hand hold easily. I was hand holding to 10x magnification today, albeit half resting on a surface (MP-E at max + 2x).
Interesting about the aperture. I was using a flash -- 580 EX II -- at exactly 1/200. Still, at extreme close-ups of subjects...I did not have much luck keeping it steady.
I also found manual focusing was an absolute must. Normally with Macro I like to manual focus anyways, but I sometimes use autofocus to get an approximate...but this lens combo did not want to focus at all. It just kept hunting and hunting.
Anyways, it's cool that this can be done. Gotta love tinkering with all the equipment. Thanks for the help.