The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Nikon 18-135mm f3.5-5.6G ED-IF and the Sigma 18-125mm F3.8-5.6 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. Sigma 18-125mm F3.8-5.6 DC OS HSM is the longer of the two lenses at 89mm. The Nikon 18-135mm f3.5-5.6G ED-IF with a length of 87mm, is 2mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 74mm.
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. Nikon 18-135mm f3.5-5.6G ED-IF weighs 385g, which means it is 105g (21%) lighter than the Sigma 18-125mm F3.8-5.6 DC OS HSM which has a weight of 490g.
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
Both the Nikon 18-135mm f3.5-5.6G ED-IF and the Sigma 18-125mm F3.8-5.6 DC OS HSM have the same Filter thread size of 67mm.
Below are links to the 67mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Nikon 18-135mm f3.5-5.6G ED-IF and the Sigma 18-125mm F3.8-5.6 DC OS HSM 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
Nikon 18-135mm f3.5-5.6G ED-IF has a focal range of 18-135mm and
7.5X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-202.5mm when used on a APS-C / DX format camera.
On the other hand, the 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.