Originally posted by tubamatt Thanks guys. I decided to stay with the kit lens 18-55mm for a while, because I looked at some sample pictures of the Sigma 17-70mm but they seem to me less sharper than my kit lens
The Sigma lens itself is sharper when making an controlled back-to-back comparison. But what you have demonstrated nicely is that the lens itself is very seldom the main determining factor. The shutter speed, focus distance, aperture, steadiness of the photographer's hands or tripod, ISO, camera used, camera settings used, post processing applied, the lighting, the nature of the scene itself - all of these have a *huge* impact on the sharpness of the resulting photo. All else equal, the Sigma *would* produce slightly sharper results, but in the pictures you looked at, all else was *not* equal. And this suggests that if you want sharper pictures, while you *could* buy a sharper lens, simply working on mastering those other elements will often make a bigger difference.
Which is to say, I agree with your decision to stick with the 18-55 for now, but if at some point in the future you've mastered everything else to the point where it does become clear that the lens itself is what is holding you back from further advancement, then don't rule out the Sigma 17-70. On the other hand, there are other lenses that would be better still - but maybe not as much flexibility for the money.