OK, so what we’re gonna do is take the best all-around supertelephoto lens made (the original Canon 500mm f/4L IS) and make it a little sharper. Then we’ll fill it with helium or something to make it 20% lighter while we do that. Let’s put in an extra stop or so of image stabilization while we’re mucking about. Oh, and we’ll design it so it loses almost no image quality with the 1.4X III teleconverters.

Did they pull it off? Yep, absolutely. Is it better than the previous version? Yep, absolutely. Although in this case the differences are small and subtle. Is it worth the price difference? I’m not certain if it is in your case. For me? Well, all I can say is the weight difference is the difference in “I can handhold this with no problem if the light’s good” and “I can handhold this long enough to mount it to my tripod”. Sure, I should shoot it mounted to a nice sturdy tripod. But there’s nothing quite as sweet as walking up to someone straining to mount their lens on their tripod, pulling this up to my shoulder, taking a few shots and giving them that “poor girly-man weakling” look.
January, 2013