I don’t have the means to test, but I’ve always wondered if the first generation Maxxum “Big Beercan” 75-300mm zoom is better than the current-generation Tamron and Sigma 70-300mm’s for the A850. At 12 and 16 mp the “Big Beercan” has slightly better corner sharpness than a Sigma or Tamron 75-300mm, especially wide open and at the long end of the zoom. But it does much worse in the area of chromatic aberration, the so-called purple fringing. What I wonder is if the sharpness advantage increases with pixel density. The 70-300 third party zooms are close to their resolving limit already at 12 megapixels. The first generation Maxxum zooms are not. But can they resolve more than required by a 25mp sensor? I don’t know, but I’d be very curious. If the “Big Beercan” stays tack sharp at 300mm, wide open on a 25mp sensor, then it may be worth the tradeoff with the purple fringing for most shooting situations. Most pictures do not present a situation where the purple fringing shows up in any significant way. Purple fringing is mostly on very high contrast edges, and it can be controlled a bit in raw image processing. Of course high-end zooms (in the $1000-3000 range) will allow you to avoid the trade-offs, but that is a lot of $$ worth of equipment to carry around all day.