After my recent purchase of the Nikkor 70-300mm lens - which was intended as a cheap way to find out if I would like a zoom lens - I now purchased an upgrade on this based on my experience with it - the Sigma 28-300 Hyperzoom.
The Nikkor is a good lens though it suffers from heavy Chromatic Aberrations, especially at 300mm and in high contrast areas. The problem with a 70-300mm lens is that it does not start wide enough for holiday or walk about type shots, I often found myself wanting to change lens to my 18-70mm to get certain objects in frame that was too close or too big.
The 28-300mm is a good middle ground lens, I used it a bit today and found that I was unable to produce any CA and that I was not tempted to swap to a wider lens ever. Lens swapping on DSLR's are notorious for getting dust on the CCD which requires rather scary cleaning using expensive CO2 based systems or cleaning swabs. The 28-300mm gives the equivalent of a 10x magnification when quoted in the typical digital camera speak. The lens was a bit hard to find, but eventually I found a dealer with stock and paid £200 for it.
View the full entry for a photo of the lens, also my first attempt at a studio type shot using some black cloth and a desk lamp, will need to get some velvet.
I have a canon rebel autofocus with builtin flash. Is the 28-300mm 3.5-6.3 ASF lens the same as the ASF IF lens, and if not what is the difference between the two? Is one sharper than the other or are they the same lens?
Tyrone, in answer to your question there is virtually no difference in quality between the two lenses. What makes the IF lens different (and generally more expensive), is that it is an Internal Focus lens. This means that the front of the lens does not rotate when the lens is focusing. This avoids messing up your filters whenever you focus the lens.