It is just simply a very good lense, nice clean crisp images, its quick to auto focus (a little noisey) but very functional, the zoom is smooth and the manuel focus is a doddle to use, for the money, you can not go wrong, i would recommend this lense to anyone. i would just like to add that this lense works very well and 100% effective with the Canon eos 400d dslr camera.
For value for money this lens would be hard to beat! Build is not up to top professional lenses and focusing is a bit slow and noisy, but accurate. However the quality of the images it produces belies it's modest price. It is easily as sharp as my Nikon lenses and the macro facility is very handy at times when doing studio work. For light use you will not be dissapointed with this lens.
Sometimes a lens can try to be too much at once - most of the time, the best ones you can buy for the job are the dedicated ones. This can however, turn out to be very expensive.
This lens has so far worked out very well for me. I stumbled on it looking for a dedicated macro lens on a budget. Although its not quite up to the dedicated macro lenses, it produces some pleasing results and has so far been more than worth its money. The ratio is 1:2 (a bit out from the usual 1:1 of a dedicated macro lens) giving pleasing results. The lens has also come into its own for my landscape work.
I would recommend this for any photographer on a bit of a budget and looking for something for most occasions!
N. B. I am currently using this on a D40x which means the lens is not compatible with the autofocus although is still easy to use due to the ease of the focusing.