This is the Sigma 50-200mm DSLR telephoto zoom lens designed for Nikon cameras with a "Nikon F" mount as well as other compatible cameras.
It features a lens aperture of F4-5.6, 4x optical zoom, and a 55mm thread size (which can been changed by using stepping rings if necessary.) The biggest selling point of this lens however is the optical image stabilization and Hypersonic motor - both of which is a surprising but welcome addition to a "budget lens."
It does however have its problems that no doubt reflect the price tag. Some images lack sharpness and also produce results that seem soft in places. Chromatic aberration and even some barrel distortion does occur towards the telephoto end of the lens that is difficult to compensate for. Finally focusing can be a problem in low light conditions.
However there are plenty of redeeming features here that save the lens. I've already mentioned the OIS and HS motor, but build quality is pretty good. It feels solid constructed of plastic and rubber but it's not overly lightweight or heavy (coming in at just over 400g). It excels at portraits especially at 50-70mm focal length, and the Super Multi-Layer Coating does manage to reduce flare and helps to improve contrast (without having to pay extra for a UV filter or similar). Giving the right conditions and some time and some practice it is possible to produce some stunning images.
It offers manual and automatic focus, and it is easy to switch between the two. The auto focus will do it's job well most of the time (with a few exceptions such as low light when it tends to be down to a matter of luck).
Also worth a note is the whisper quite motor, which helps you to take pictures of wildlife without disturbing them, and the image stabilizer built in to the lens does work well (so you don't have to worry about blur.) For me it is the IS system that is the icing on the cake as it's difficult to convey in words how well it works when shooting by hand, but trust me when I say that it is a really impressive system.
It doesn't come with any extras such as a lens hood or lens pouch, but for just over £150.00 (correct when buying and reviewing) it still represents great value for money when taking into account what is included and the possibilities that it presents.
Overall I really enjoyed using this lens with my camera, and it has allowed to to capture some of my best images of all time. It's refreshing knowing that you don't have to pay twice the price of your DSLR to get a decent lens. So if you're looking for a budget telephoto zoom lens this is one of the better ones that I've seen in recent times and is well worth short listing.
If your looking for something with a bit more 'reach' then I would go for the Sigma 70-300mm f4-5.6 DG lens which also offers macro. It's a bit more expensive and doesn't have quite the same potential as this lens however its still worth considering.
You can buy this lens from Amazon.co.uk for £169.29 or from Jessops for £189.00.
(I'm a reviewer on Amazon, and some my reviews are copied from there to dooyoo. Please feel free to check out my Amazon profile under my real name of Mr Andrew M Kerr.)