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 24-120mm f3.5-5.6G ED-IF VR 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 18-125mm F3.8-5.6 DC OS HSM with a length of 89mm, is 5mm 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 18-125mm 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 85g (14%) lighter than the Nikon 24-120mm f3.5-5.6G ED-IF VR which has a weight of 575g.
Filter Threads
The Sigma 18-125mm F3.8-5.6 DC OS HSM has a filter size of 67mm whereas the Nikon 24-120mm f3.5-5.6G ED-IF VR 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 24-120mm f3.5-5.6G ED-IF VR:
Lens Mounts
The Sigma 18-125mm F3.8-5.6 DC OS HSM has the Nikon F (DX) lens mount whereas the Nikon 24-120mm f3.5-5.6G ED-IF VR has the Nikon F (FX) lens mount. Some of the latest released cameras that are compatible with these mounts are Nikon D3500, Nikon D7500 and Nikon D5600 for the Nikon F (DX) Mount and Nikon D6, Nikon D780 and Nikon D3500 for the Nikon F (FX) Mount.
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 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.