Well, the new Tamron 28-75 f/2.8 arrived just before the weekend. Although all glass in the house is technically "community glass" shared between mine and The Wife, the Tammy is destined to be the primary lens for her 50D. Ideally, this well-regarded lens will 1) maximize the image capabilities of the 50D without breaking the bank, and 2) let me have my 28-135 IS back, since The Wife has all but commandeered it for her camera.
So, I haven't actually been able to test out the Tammy yet, other than taking a few quick low-light shots to test its speed. She, on the other hand, has been working it hard. From what I can tell, the AF doesn't have any significant problem locking on in low light conditions, which was the one recurring concern we'd seen in otherwise glowing reviews for this lens. AF is fairly quiet, too--not silent like USM, but a mere whisper when compared to something like the Nifty Fifty. The MF grip does rotate during AF, which is very annoying, but you get used to that very quickly and instinctively learn the best way to hold it.
Initial indications are that this is indeed a sharp lens. Haven't gotten around to pixel-peeping yet, but the images look crisp. Contrast does seem better than the 28-135. And yes, the Tamron lens cap is by far the best design on the market!
These are just preliminary impressions. The Tammy hasn't been micro adjusted on the 50D yet, so that could improve things considerably. But it looks like the Tamron lens is equal, if not superior, to the 28-135 in most areas. Looks like I've got my main lens back...

.


