Evening All, I've recently bought the Tamron 17-50 f2.8 in Sony Alpha Mount off of ebay, I paid a good price (£110), which included postage. To look at the lens looks mint and testing over the weekend has been as expected; exceptional, and a very close match for the Sony 16-50 which I've had in the past. Optically all the photo's shot with it have been as expected, and yes I'm very pleased with the results, and the focusing is fast and assured however; the lens hood was very stiff when parked or fitted, lens cleaner around the bayonet fixings did drastically improve the play however things seems to be tightening again, but the worst thing and the reason I'm writing are the half a dozen or so artifacts on the inside of the rear element, it doesn't look like fungus and being on the inside, and they don't seem to affect Image I.Q at all. I'm at a bit of a loss as to what it is, how to remove them (if possible), and given that I'm within the time frame of returning the lens; would like to know if it's likely to get worse and more importantly if it's going to degrade IQ. It's unlikely, but not impossible that I'd get another 17-50 f2.8 for the same or less and it's definitely producing the goods, but is it a keeper or go-er ?. Any info or advice would be greatly appreciated, as to what the artifacts are and the best way off freeing up the lens hood is.