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. Many 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. 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. Giving the light conditions and some practice it is possible to produce some stunning images.
Also worth a note is the whisper quite motor, which helps you to take picture of wildlife without disturbing them, and the image stabilizer does work well.
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.
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.