Cheap Sigma AF 18-200mm f/3.5-6.3 DC OS (Optical Stabilizer) Zoom Lens for Nikon Digital SLR Cameras

Sigma AF 18-200mm f/3.5-6.3 DC OS (Optical Stabilizer) Zoom Lens for Nikon Digital SLR Cameras
The Sigma 18-200 F3.5-6.3 DC OS HSM Lens incorporates an Optical Stabilizer function and is exclusively designed for digital SLR cameras. It is perfectly suitable for low-light conditions; whether indoors, at dusk, or in the telephoto range. This system uses two sensors inside the lens to detect vertical and horizontal movement of the camera, and effectively compensates for camera shake by moving an optical image-stabilizing lens group. It also automatically detects panning movement of the camera and compensates for camera shake when shooting moving subjects such as motor sports. SLD (Special Low Dispersion) glass and aspherical glass provide excellent correction for all types of aberrations. This lens has a minimum focusing distance of 45cm (17.7") throughout the entire zoom range and has a maximum magnification of 1:3.9. Since the inner focusing system means the front of the lens does not rotate, optional circular polarizing filters and the supplied petal-type hood can easily be used. A magnification scale is displayed on the lens barrel, ensuring ease of use. A zoom-lock switch mechanism is provided to prevent the lens from creeping due to its own weight. 69.3 - 7.1 degrees (Sigma SD format) angle of view 7 Diaphragm Blades F22 Minimum Aperture 45cm / 17.7 Minimum Focusing Distance 1 - 3.9 Maximum Magnification Petal Lens Hood Fully compatible with All Nikon Digital SLR cameras including the D40 and D40x Dimensions - Diameter 79mm x Length 100mm Weight - 21.5 ounces (610 grams)

Customer Review: 3.5 would be more accurate

I have had this lens since 9 July, and used it without incident until 25 July, when the OS failed. Up to that point, I would have given this lens a five-star rating without the slightest hesitation. The distortion control, as well as the sharpness on the first sample were excellent. Furthermore, the focus was accurate to a T in all situations, including very low light.
The replacement lens, which I have now used for about a week, does not have nearly the same sharpness at the edges. It is fine in very bright light, but in dimmer situations, both the sharpness, and the focussing ability, are not up to the standard of the first sample.
I also find that the OS on this sample does not give the same f-stop compensation as on the first one.
This said, the lens remains a good one, and I would still recommend it for use with the Nikon D40.
Whether or not I will retain this one, or again request a replacement based on the less than stellar focussing ability in low light/low contrast situations remains to be seen.

Customer Review: excellent lens

I have tried many lens with my 40D. I like the 18-55mm IS kit lens. It's probably the sharpest standard lens that Canon ever made. 28-135mm IS is also good, but lack of 18-27mm zoom. I sold it and bought the Sigma 17-70mm and Sigma 18-125mm OS. I returned 17-70mm because I have shaking hands and most of my photos are indoor. I also returned 18-125mm because it produce very very soft and lack of contrast. Almost like older P&S digital camera. I then bought the Tamron 17-50mm f/2.8. Hoping the f/2.8 will help with my shaky hand and indoor situation. I return it after compare to my 18-55mm IS. Not worth the extra $300 for Tamron for the same zoom. Finally, I decide to buy the Sigma 18-200mm OS after reading many positive and negative reviews. To my surprise, 18-200mm is very sharp lens in ALL ranges. I read that lens can be soft at certain zoom. I have tried for a week to try to find the soft spot, I can't find it. The only thing I noticed is the "strong" OS motion. I can really see the OS kicks-in. I was surprised that I got almost all keepers in my "walking" shots. Highly recommended. I don't know if any lens in this range can be better, especailly with OS.