im considering buying this lens and have a couple basic questions. Basically the F2.8 IS version would be ideal, but out of my price range. As is the F4 IS version. I found one of the F4s for sale locally at a good price... basically this will be my first SLR lens. Ill be using a Canon XTi. Since its my first SLR the only thing I have to compare it to is my Canon S2 point and shoot. My concern is the NON-IS. Im not worried about the F4 as much because I can get a smaller fast prime for that 'blur effect'... but without the IS im wondering how hard is it to use full tele and not get shaky pictures??? with my canon s2 it has some kind of built in IS and at full telephoto, its still darn near impossible to get a smooth shot without a tripod... will it be about the same or even worse?