The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Nikon 24-120mm f3.5-5.6G ED-IF VR and the Sigma 18-200mm f3.5-6.3 II DC OS HSM 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 24-120mm f3.5-5.6G ED-IF VR is the longer of the two lenses at 94mm. The Sigma 18-200mm f3.5-6.3 II DC OS HSM with a length of 88mm, is 6mm shorter. Besides being longer, the Nikon 24-120mm f3.5-5.6G ED-IF VR also has a larger diameter of 77mm compared to the Sigma 18-200mm f3.5-6.3 II DC OS HSM's 75mm 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 18-200mm f3.5-6.3 II DC OS HSM weighs 490g, 14% (85g) lighter than the Nikon 24-120mm f3.5-5.6G ED-IF VR's weight of 575g.
Filter Threads
The Nikon 24-120mm f3.5-5.6G ED-IF VR has a filter size of 72mm whereas the Sigma 18-200mm f3.5-6.3 II DC OS HSM has a 62mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 72mm filters that we recommend you to consider for the Nikon 24-120mm f3.5-5.6G ED-IF VR:
And these are the 62mm filters that we recommend for the Sigma 18-200mm f3.5-6.3 II DC OS HSM:
Lens Mounts
The Nikon 24-120mm f3.5-5.6G ED-IF VR has the Nikon F (FX) lens mount whereas the Sigma 18-200mm f3.5-6.3 II DC OS HSM has the Sigma SA lens mount. Some of the latest released cameras that are compatible with these mounts are Nikon D6, Nikon D780 and Nikon D3500 for the Nikon F (FX) Mount and Sigma SD1 Merrill, Sigma SD1 and for the Sigma SA Mount.
Sigma 18-200mm f3.5-6.3 II DC OS HSM is also available in Canon EF and Nikon F (DX) mounts.
Focal Range
Nikon 24-120mm f3.5-5.6G ED-IF VR has a focal range of 24-120mm and
5.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
36 - 180mm.
On the other hand, the Sigma 18-200mm f3.5-6.3 II DC OS HSM 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.
