Pixel-peeping considered harmful
“Pixel-peeping” is the practice of examining a photo on a computer screen at 100 % resolution (one photo pixel equals one dot on the screen).
While there may be good reasons for doing this, this practice has also caused inexperienced photographers no end of grief because when you do this, any flaw (softness, CA, coma, noise) in the photo will be very visible.
Unless you've had enough experience with digital photography to have a sense of reality, any photograph will be perceived as flawed when pixel peeping. As a result, pixel-peeping photographers may think that their lenses are broken or useless. In reality, a photo that looks horrible when viewed as a 100 % crop on the screen, will still appear tack sharp when printed on photo-paper.
So if you've just started pixel-peeping and find that your photos are not really sharp, pause to print your photos before you run out an buy that professional grade lens. You may discover that your present kit is OK.