Originally posted by El Bolson I've seen a Sigma 28-200 AF on ebay for pretty cheap (IMO) and am curious if anyone has had good experiences with this lens...
The *only* superzoom (eg, more than 3-4X) considered on a par with the 50-200 would be the Tamron/Pentax 18-250 (eprhaps Sigma too; it's too new for a consensus to have developed).
Here's a basic rule to consider: for a given price, the lower the zoom factor the better. That is, a $250 prime will be better than a $250 3X zoom, which will in turn be better than a $250 6X zoom, which will in turn be better than a $250 10X zoom. To get a 10X zoom that compares in quality to a 3X one, you should expect to pay much more for it. In fact, you could probably get a pretty good predictor of lens quality by taking the price and dividing it by the zoom factor.
So there is very little chance any inexpensive 28-200 is going to come close to a similarly priced 50-200. Again, as a *replacement* for your 18-55, it might be sort of interesting, as you would gin a lot at the long end, but you'd give up quite a bit at the wide end too. But it would make for fewer lenses changes - you could leave the 28-200 on the camera most of the time, switching to the 18-55 only when you need something wider. Quality would no doubt be not as good as the 18-55 + 50-200, but maybe good enough to be a good tradeoff for the convenience if you're of that mindset.