I recently decided to order a Panasonic 100-300 to satisfy my long tele needs in a more compact package than my Canon APS-C gear. I was a bit hesitant, because in photos this lens look really big, and since the main reason I started using m43 was to save weight (not size, particularly), I wasn't sure I was going to like this lens. Well, when I opened the package, I did indeed react to the size and weight. In a very positive manner! I'm amazed at just how small this is for a 600mm f/5.6 equivalent lens. (And don't start talking to me about DOF, etc. DOF is plenty shallow for my needs.) So what do I mean be equivalence? See the image below. The Canon is a mid-sized 50D with a 70-200 f/2.8 + 2x TC. At the long end, that's 200x2x1.6 or 640mm f/5.6. (If this were a Nikon, it would be 200x2x1.5 or 600mm f/5.6.) The Panasonic is a GH3 with a 100-300, so that's equivalent to a 600mm f/5.6. Pretty much the same FOV and f-stop. Who says the GH3 and 100-300 is "too big"? The one thing I still need to test is AF. For C-AF, the 100-300 clearly isn't as fast as the 70-200 itself, but when you add the TC the system slows AF for better accuracy. And the GH3 AFs better than any other currently available m43, so I'm curious to see how they compare. Maybe this weekend I'll have some time to test. If this will keep up for auto racing, my Canon gear will rarely see any use.