The crops in this chart were from images shot in raw using a 30D with sharpness set to 0, using the center focal point. They were converted with Canon DPP, then cropped from the center and resized. No other editing was performed (I did not rescale the 280mm images, hence, they are slightly smaller than the 300mm images). To make it a fair fight, I used a monopod with the Canon 70-200mm and the Tamron 70-300 lenses to balance the IS of the 300mm lens. I was approximately 30 feet from the thermometer. I took 3 shots at each setting and chose the best to display here. From these pictures, I'm pretty pleased with the results. Both L lenses appear to have slightly lower sharpness/contrast at larger aperature and the 300mm lens seems a bit sharper overall than the 70-200mm + 1.4TC combo, but the difference isn't too great. The Tamron doesn't perform as well and shows some degree of CA wide open, but I think it does great considering what it costs, the range of the zoom, and how light it is. I have since field tested the 70-200mm lens with the 1.4X extender along side the 300mm lens (with and without the extender) at the Buffalo Bills training camp. All combinations seemed to be effective. To view some of these pictures, go to my Buffalo Bills Training Camp gallery. I have more recently used all three lenses to take pictures at a motorcycle race on an overcast day. All lenses did quite nicely. Go to my Canada Superbike gallery for images taken with the two Canon lenses or to the Canadian Superbike 2006 gallery for images taken with the Tamron.