This is a comparison of three lenses at 50mm (one is actually at 55mm): the Canon EF 50mm f/1.8 II, the Canon EF-S 18-55mm f/3.5-5.6 II, and the Tamron SP AF 28-75mm f/2.8 XR Di. The crops below were from images shot in raw using a 30D with sharpness set to 0, using the center focal point. They were converted using Canon DPP, then cropped from the center and corner. No other editing was performed. It is necessary to view the comparison charts at full size to see any differences. I noticed a few things. First of all, the EF 50mm f/1.8 lens is somewhat soft in the center and corners at f/1.8-f/2.0, but sharpens up nicely by f/2.8. This is not a surprise. Second, the Tamron images are somewhat yellow compared to the Canon images. I had heard this about Tamron lenses, but had not definitively identified this in my own lens until now (obviously, it hasn't bothered me much). Third, the Tamron is pretty sharp in the center and slightly soft in the corner at f/2.8, then sharpens up nicely as it is stopped down. Finally, the Canon kit lens is pretty sharp from f/5.6 through f/11, which comes as a bit of a surprise. It's a little softer in the corners, particularly at f/5.6, and the images have less contrast than the other two, but overall it performs quite well, especially considering that it added only $40 to the cost of my 30D. I use all three of these lenses and have been satisfied with all three. Now I know why.