The 550D has an amazing feature for video - much the same as cropping for stills - but it allows you to be getting the equivalent to around a 4500mm (!!!) lens for SD (not HD) video but I guess it may appear on one of the next pro spec cameras too. Basically it crops the video to give 7x magnification but still deliver 640x480 resolution
On 550D, the 70-200 lens is equivalent to 112-320 due to the crop, then with 2x teleconverter it goes 224-640mm, with the 7x magnification that makes it 4480mm. I'll be putting some samples on YouTube once I've edited them but quite stunning zoom capability.
