The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-125mm F3.8-5.6 DC OS HSM and the Nikon 18-200mm f3.5-5.6G ED VR II for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Nikon 18-200mm f3.5-5.6G ED VR II is the longer of the two lenses at 97mm. The Sigma 18-125mm F3.8-5.6 DC OS HSM with a length of 89mm, is 8mm shorter. Besides being longer, the Nikon 18-200mm f3.5-5.6G ED VR II also has a larger diameter of 77mm compared to the Sigma 18-125mm F3.8-5.6 DC OS HSM's 74mm diameter.
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Sigma 18-125mm F3.8-5.6 DC OS HSM weighs 490g, which means it is 75g (13%) lighter than the Nikon 18-200mm f3.5-5.6G ED VR II which has a weight of 565g.
Below you can find the dimension and weight table of the SuperZoom Lenses in Nikon F (DX) Mount for size comparison purposes.
Superzoom Lenses in Nikon F (DX) Mount for Size Comparison
Filter Threads
The Sigma 18-125mm F3.8-5.6 DC OS HSM has a filter size of 67mm whereas the Nikon 18-200mm f3.5-5.6G ED VR II has a 72mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 67mm filters that we recommend you to consider for the Sigma 18-125mm F3.8-5.6 DC OS HSM:
And these are the 72mm filters that we recommend for the Nikon 18-200mm f3.5-5.6G ED VR II:
Lens Mounts
Both the Sigma 18-125mm F3.8-5.6 DC OS HSM and the Nikon 18-200mm f3.5-5.6G ED VR II has the same Nikon F (DX) lens mount. Some of the latest released cameras that are compatible with the Nikon F (DX) lenses are Nikon D3500, Nikon D7500 and Nikon D5600.
Sigma 18-125mm F3.8-5.6 DC OS HSM is also available in Canon EF and Sigma SA mounts.
Focal Range
Sigma 18-125mm F3.8-5.6 DC OS HSM has a focal range of 18-125mm and
6.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-187.5mm when used on a APS-C / DX format camera.
On the other hand, the Nikon 18-200mm f3.5-5.6G ED VR II has a focal range of 18-200mm and 11.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-300mm when used on a APS-C / DX format camera.