I purchased this lens at the same time as my Sony a33 with 18-55mm kit (see review seperately). I wanted a lens that would capture pictures of friends windsurfing some way offshore, but I did not want to spend megabucks. I have a 70-210 Minolta lens which I hoped would do the job, since the 35mm equivalent works out at 105-315mm (apply the 1.5X magnification factor) but it did not get quite close enough. It still does produce, very good quality images though and I am reluctant to let it go.
I read that the 70-300mm Sony G lens is fabulous, but having laid out the thick end of £600 on the a33, I could scarcely justify almost the same again no matter how good the lens was. I paid £179 for this Sony 70-300mm lens from Comet, so the current £175 price tag is pretty good. I had the advantage of Sony VAT cashback on the camera and lens so it was a competitively priced package. I was expecting an OK if not blistering performance from what seems to be a budget lens, but was very surprised at how good my results were. You do need good light for the best results, as the maximum aperture is f4.5, but the a33 has a quite useable ISO 3200 capability to offset this. I found the sharpness to be acceptable at minimum zoom, and improving to very good at maximum.
The 35mm equivalent works out at 105-450mm, and I now have more than enough reach for those offshore shots. It is also great for candid shots of our little neices and nephews as you are far away enough for them not to see the camera, and so they act naturally.
All in all I am very pleased with this lens. It is well made, quite heavy. In fact it feels a lot like the old Minolta lens in terms of construction. I would recomend it over the Sigma zoom for a33 users due to the need for rechipping of the Sigma lenses to work with Sony SLT cameras. I would rate the results better than my 70-210 Minolta, but of course this lens is designed for digital, with extra coatings etc.
As always I recomend protecting your investment(especially if using it on the beach!) with an inexpensive UV filter. I have found Hama products to be ideal and well priced from Amazon.