I'm new to digital, so please bare with me. I have a 20D. When I shoot with my Tamron 70-300 (f4/f5.6), and I zoom long to 300 mm or near 300 mm, with autofocus on, the images that I download and view in Photoshop Elements seem a little on the soft side when viewed at 100%, even where my focus point was when I took the shot. At 70 mm or 135 mm (+/-), things look a little crisper. The same is true with my Sigma 170-500 (f5/f5.6). The Sigma images that I'm thinking of were taken at 1/1600 on a sunny day, without a tripod, but supported by a fence. The Tamron images were taken from a tripod and a remote switch. I took the shots in large JPG format on the 20D. I don't know much about Photoshop, but the instructor in a class I'm taking told us that with a large format JPG on a 20D (or other cameral with 8+ megapixels), we can print images up to 16" X 20". If I were to print the images that I referred to at that size, would I see some of the softness that I mentioned? Is the depth of field just so small at those focal lengths that I'm missing it? Or is it a limitation of the lens? Is it both? Am I expecting too much from the lenses to be able to print something that large at that focal length? Don't get me wrong, the softness at 100% at those focal lengths doesn't seem to be unacceptable, it's just that I know things can look sharper because I've seen images shot under the same lighting conditions, but at a smaller focal length. Would I even notice the slight softness that I do at 100% on the long focal length shots when I print at a more reasonable size, say 8X10 or 5X7? I'd experiment, but I don't have a photo printer yet. Sorry to be so much trouble. Thanks for the help.