The test shots were taken using a Nikon D300.

Nikon Lens was the AF-S Nikkor 18-200mm 1:3.5 – 5.6 G ED with VR

Sigma Lens was the Sigma DC 18-200mm 1:3.5 – 6.3 D

In all test shots Normal VR was active and the camera was hand-held.

For the first test, I took two pictures of a flower, one with each lens.

The second test was a photo of a clock tower in the distance.

I have cropped all 4 photos to show specific detail of the photo.  You can click the photos to open up a larger image.

The Flower Photos:

Nikon Lens Model: NIKON D300 Date & Time: 2009:05:12 12:20:12 Exposure Time: 0.003125 F Number: 9.0 Exposure Program: program normal Bias: 0/6 Metering Mode: multi-segment Light Source: auto Flash: No Focal Length: 200.0 ISO: 200	Sigma Lens Model: NIKON D300 Date & Time: 2009:05:12 12:20:46               Exposure Time: 0.003125 F Number: 9.0 Exposure Program: program normal Bias: 0/6 Metering Mode: multi-segment Light Source: auto Flash: No Focal Length: 200.0 ISO: 200

The Clock Tower Photos:

Nikon Lens Model: NIKON D300 Date & Time: 2009:05:12 12:20:17 Exposure Time: 0.0025 F Number: 10.0 Exposure Program: program normal Bias: 0/6 Metering Mode: multi-segment Light Source: auto Flash: No Focal Length: 200.0 ISO: 200	Sigma Lens Model: NIKON D300 Date & Time: 2009:05:12 12:20:50 Exposure Time: 0.002 F Number: 11.0 Exposure Program: program normal Bias: 0/6 Metering Mode: multi-segment Light Source: auto Flash: No Focal Length: 200.0 ISO: 200

I’ll leave you to draw your own conclusions, but from these and a few other test pictures I have taken the Sigma lens focus is better on close objects at 200mm, while the Nikon is easily better at the distant object and focal length of 200mm.