This is one of the cheapest lens in this category and is available in Canon, Nikon, Pentax, Sigma and Sony mounts...
Sigma 18-200mm f/3.5-6.3 DC Review
This is one of the cheapest lens in this category, and it’s available in Canon, Nikon, Pentax, Sigma and Sony mounts. It doesn’t offer image stabilisation, and so is best suited to cameras with on-board IS.
Consisting of 15 elements in 13 groups, it includes two Super Low Dispersion (SLD) elements and two hybrid aspherical optics to deal with distortion. Compared with some others, this is a relatively simple lens at a reasonable price.
Its small size and light weight make it useful for travelling, while the zoom operation is fluid, only losing a little traction at 200mm. It’s among the noisiest with regards to focusing.
This lens does a great job at controlling chromatic aberrations at 200mm, with a blinding result at the centre and above average in the corner. Elsewhere the lens puts in a lacklustre performance, with the chromatic aberration readings at 18mm at about average for this type of lens. The resolution, while peaking at nearly 1200lwpph at f/4, rapidly fall offs into mediocrity. At 200mm, the low resolution is matched only by Nikon’s alternative.
A bit of a disappointment with inconsistent performance