Sigma 18-200mm F3.5-6.3 DC OS

The Sigma AF 18-200mm f/3.5-6.3 DC OS is an extremely versatile lens but performance-wise it is a bit of a mixed bag. The resolution characteristic varies significantly throughout its immense zoom range. Interestingly the extreme ends are actually the sweet spots of the lens whereas the 35mm setting is downright miserable at large apertures. The quality recovers at 50mm before dropping somewhat at 100mm again. To be fair the lens is capable to provide a decent quality if you avoid large aperture settings and stick to ~f/9 regardless of the zoom position. On the positive side vignetting and CAs are quite well controlled and distortions may be a problem at 18mm only. The quality of the bokeh (out-of-focus blur) is sometimes less than stellar though. The AF speed and accuracy is pretty fine and the image stabilizer can give you an advantage equivalent to about 3 f-stops in field conditions. The build quality of the Sigma is surprisingly good and above average for a lens in this class.