I bought this lens this weekend to use on my Rebel XTi. I want to use this lens mostly for photographing wildlife. I took about 60 shots with it this weekend to see what kind of pictures I can get out of it. The problem I am having is that I cant seem to get good sharp images at anywhere near the full zoom. I do get good sharp, well focused images at 170mm, but that is not why I bought the lens. Im not a pro photographer and this is my first telephoto lens over 200mm, so I am not sure if the problem is me or the lens. I was shooting in good daylight at iso 400, F8 (which is supposed to be the sweet spot for this lens), distances from 25 to 100 feet, using a tripod and remote shutter release. Shutter speeds ranged from 1/250 to 1/1000. When I open the images in Camera Raw they look OK at the default 21% zoom ratio, not perfectly sharp, but respectable. However, when I zoom to 100% the image is not sharp and seems not perfectly focused. Sharpening the image doesnt completely fix the problem. Am I expecting too much from a telephoto zoomed to 500mm or is this lens just not capable of taking sharp images at this setting? I have 10 days to return this lens, and I am currently disappointed enough with it to return it. I just want to make sure it is not what I am doing or that I have expectations that are beyond what is capable with a 500mm lens.