I can tell you from experience, don't. The cut-rate brands sold on Ebay (Phoenix, Opteka etc..)and elsewhere are simply junk. It's not that the photos taken with the the off-brands lenes are just bad and corectable via Photoshop, it's that they SO bad, that the autofocus on my Sony 717 simply can't self-correct enough to make the lenes even usable.

The VCL-HGD1758 works perfectly with very little/no loss of quality. I ended up buying one after trial and error. Learn from my mistake!

Your other options for a fine lens at about half the price are are the Olympus TCON-14B, Olympus TCON-17, Olympus B-300 and the Olympus A-200. They all work equally well on the Sony 707,717 or 828 but any of these non-Sony lens will require an adapter or step-ring to compensate for their non-58mm threads.

This is a great, albiet costly product. I sometimes question my own wisdom in buying a lens that is about 1/3 the price of the camera for only a 1.7X improvement in zoom (from 5 to 8.5 zoom) but I can't fault the quality.