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 HSM and the Sigma 17-50mm F2.8 EX 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 17-50mm F2.8 EX DC OS HSM is the longer of the two lenses at 92mm. The Sigma 18-125mm F3.8-5.6 DC HSM with a length of 89mm, is 3mm shorter. Besides being longer, the Sigma 17-50mm F2.8 EX DC OS HSM also has a larger diameter of 84mm compared to the Sigma 18-125mm F3.8-5.6 DC 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 HSM weighs 490g, which means it is 75g (13%) lighter than the Sigma 17-50mm F2.8 EX DC OS HSM which has a weight of 565g.
Filter Threads
The Sigma 18-125mm F3.8-5.6 DC HSM has a filter size of 62mm whereas the Sigma 17-50mm F2.8 EX DC OS HSM has a 77mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 62mm filters that we recommend you to consider for the Sigma 18-125mm F3.8-5.6 DC HSM:
And these are the 77mm filters that we recommend for the Sigma 17-50mm F2.8 EX DC OS HSM:
Lens Mounts
The Sigma 18-125mm F3.8-5.6 DC HSM has the Pentax KAF3 lens mount whereas the Sigma 17-50mm F2.8 EX DC OS HSM has the Canon EF lens mount. Some of the latest released cameras that are compatible with these mounts are , and for the Pentax KAF3 Mount and Canon T8i, Canon 90D and Canon SL3 for the Canon EF Mount.
Sigma 18-125mm F3.8-5.6 DC HSM is also available in the Sony Alpha mount.
Sigma 17-50mm F2.8 EX DC OS HSM is also available in Pentax KAF3 , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 18-125mm F3.8-5.6 DC 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 Sigma 17-50mm F2.8 EX DC OS HSM has a focal range of 17-50mm and 2.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27.2-80mm when used on a APS-C / DX format camera.
