9 out of 10 points and recommendedlow cost, image quality in good light, focal length range, solid buildweight and size (comes with the focal length!)
With good light, this is an excellent performer. Don't confuse this with a f/4 $5K lens. Reasonably sharp across the entire 50-500mm range, wide open. For best sharpness 400-500mm, you should stop down from f/6.3 to f/8.reviewed March 12th, 2008 (purchased for $625)
I beat the heck out of this lens shooting college football games, all wide open, with shutter speed set to 1/800 to 1/1000 sec, from the sidelines. The zoom range was a huge asset as play ran near and far. Images were super sharp. There were plenty of pictures I would have missed with having less zoom range or having to carry (and switch between) two camera bodies.
Built like a tank, also. Solid kit.
With this lens, add a vertical grip to your camera body, you stand out from the rest of the crowd of picture takers as a serious gent. This can get you respect from the crowd milling around, and helps give you access to the vantage points you need.
If you want to use this lens for moon shots or 500mm nature shots (or any with shutter speed slower than 1/800 sec), you need to use the skills and technique required to do this well. This means using a solid tripod and head, mirror up mode, stopping down the lens a bit, and using a remote shutter release... and all in a wind protected area. Wait for the mirror vibe to settle before taking the shot, using only a remote release. If you cheat on any of these, don't expect perfection with ANY long lens.
Excellent value for money. If you work within its capabilities (i.e. F/8 or narrower at long end) and you employ proper technique, you will be rewarded with sharp, contrasty images.
8 out of 10 points and recommendedcost, weight, image stabilisation, convenience, IQ, full frameAF speed, Nikon "issues"
I bought the Nikon version, for use on the full frame D700. It replaced the Nikon 18-200/VR as my 'stay on the camera' lens when I acquired the full frame D700.reviewed November 2nd, 2008 (purchased for $600)
Sharpness of the Tamron seems to keep up with the Nikon 18-200/VR - it seems quite sharp, indeed.
Tamron's VC image stabilisation is perhaps a full stop better than the VR in the Nikon 18-200/VR. I loved the performance of the Nikon lens (especially the VR), but the Tamron's image stabilisation leaves the Nikon 18-200/VR in the dust.
Now the bad news...
1. The D700 AF (occasionally) hunts and coughs and sputters with this lens. I can't explain the reasons for this, but you'll not want to use this lens for sports action or birds in flight. Most of the time AF performance is OK, but it's not 100% - maybe 95%.
2. Some vignetting (probably only a concern on FF/FX bodies). Not a big deal.
3. On my D700, I occasionally see a lock-up problem. The D700 will indicate aperture of F/0, shutter release works - but images are completely black. According to Tamron service, this indicates communication failure between the lens and the body. This occurs maybe once every 300-400 shutter-clicks, and then power-cycling the body is required to restore normal operation. Tamron service could not duplicate the problem (I sent them my D700 for a week, to see if the problem was body-related, but no luck).
UPDATE: The lens was replaced by Tamron USA with another copy, and I've seen no re-occurrence of the lockup problem.
In short, in spite of this lens' flaws, it's the best option for a 'walk-around' lens on a FF/FX body. I don't regret buying it, and it is the lens I use most often because of its IQ and range.