Look to buy a 70-300 and you'd be overwhelmed by choice, regardless of what brand of DSLR you have, and over the years I've had my fair share, I'm currently rebuilding my lens collection, to a lesser state than before, I obviously desire a 70-300 lens, I've had the beercan (overhyped imho), sony 55-200, sigma apo dg macro, Tamron Di LD, and the Tamron USD, in stark contrast to what I've read of all these it's the APO i remember the fondest, yes build quality was horrendous; the gearing stripped just ten days after putting it on a Sony A500. I've now got an A37 (imho a massively under rated budget camera, having previously owned an A77). Yes the usd is exceptional but it weighs a ton and is huge, that hood alone is as long as the 55-200, mine also made an irritating squealing sound now and again, and then there's the price. Sony produce the 55-300 and then there's the newer Sigma OS, which has marmite reviews, my question is this, ideally to anyone who's had any of the sigma's mentioned or usd, what did you think of the lenses and image quality, sadly there seems to be no comparison on the net. I'm currently biased towards the APO because it's brand new (returnable if gearing strips) and because of it's past glories The other question relates to the plastic gearing in the Sony version of the Sigma APO DG MACRO (do other versions also have plastic gearing ?.), you can still buy the APO DG MACRO brand new for just £179 given that it's well over 5 years since my last APO, would it be safe to assume that over time Sigma replaced the plastic gearing for metal, and if not having read a lot of Dyxum reviews SLT's don't seem to have the same problem as the non Slt cameras, or do they ?.