I'm pondering purchasing the Sigma 70-200 f2.8 (the EX DG HSM Macro model) for my 20D, coupled with a 1.4x teleconverter. I think it's a cheap (compared to the alternatives like Canon L glass) way of turning the lens into a ~100-280 f4 lens equivalent. With the 1.6x crop of the 20D, that would in effect make it a ~155-450mm f4 lens, right? A similar lens (prior to 1.6x crop factor) would come in the form of something like a 100-300mm f4, that without going into any specific brands, would cost a bundle - far more than I'm willing to spend. But I can get the Sigma with 1.4x tele setup for about $1500 all up if I get it from some place like BH photo (from the 'states). I know the Simga lens is heavy, but that doesn't worry me too much.. I've been trying to think of drawbacks to this cheap tele setup, from a purely technical point of view, but can't really think of any. I'm not the type that's interested in pixel peeping, so I'm not overly concerned about having perfect image quality either - not that the Sigma has bad IQ from what I've been reading. Do you think there's anything I've neglected to think about here? Primary use would be the odd sporting event (e.g. next one is a day-nighter at the Gabba), I'll be pretty close to the action so I might be able to get away with not using the 1.4x tele so I can shoot f2.8 after dark). Besides that, some portrait stuff and bokeh experiments might be in order. Cheers, any comments / thoughts appreciated.