14 DAY TRIAL // Good news for Nikon users who like walkaround lenses since Sigma has announced an updated version to the 18-200 f/3.5-6.3 DC OS, which now has a hyper sonic motor. Unfortunately, the new lens is only aimed at Nikon DSLRs, a Canon version not being available.
For those who have drive motors in their DSLRs, this means faster autofocusing, but for D40 and D40x owners it's even better. It means that they are able to autofocus. As you might know, these two models don't have an AF motor and thus can only use AF-S lenses or other third party units that have such motors in order to achieve autofocus.
Aside from this change, the older non HSM version is identical to the newer one. Being a DC lens, the Sigma 18-200mm can only be used on APS-C sensor cameras, like the Nikon D200. However, the equivalent picture angle is that of a 27-300mm (1.5x crop factor) lens mounted on a 35mm full-frame camera.
In terms of construction, the lens comprises 13 groups with 18 elements, including three aspherical pieces to control spherical aberrations and distortions and one SLD (special low dispersion) to minimize chromatic aberrations. The overall image quality is satisfactory, but certainly nothing to brag about, especially when used wide open.
The lens design incorporates an inner focusing system, which prevents the front of the lens from rotating, making it particularly suitable for using 72mm circular polarizing filters and petal shaped lens hoods. A zoom lock switch is also provided to eliminate 'zoom creep' during transportation.
Moreover, the unit features the proprietary OS (optical stabilization) system that allows for slower than recommended shutter times to be used. This optical stabilizer uses two sensors inside the lens to detect vertical and horizontal movement of the camera and works by moving an optical image stabilizing lens group to effectively compensate for camera shake. It also automatically detects movement of the camera and compensates for camera shake when shooting moving subjects such as motor sports.
At the end of June, Sigma also put hyper sonic motors in two other lenses, the 18-50mm F3.5-5.6 DC and the 55-200mm F4-5.6 DC, again only for Nikon DSLRs.
The Sigma 18-200 f/3.5-6.3 DC OS HSM will be available for around ?440.
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