The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-35mm F1.8 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 18-35mm F1.8 DC HSM is the longer of the two lenses at 121mm. The Sigma 17-50mm F2.8 EX DC OS HSM with a length of 92mm, is 29mm shorter. On the other hand, the Sigma 17-50mm F2.8 EX DC OS HSM has a larger diameter of 84mm compared to the Sigma 18-35mm F1.8 DC HSM's 78mm 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 17-50mm F2.8 EX DC OS HSM weighs 565g, 30% (245g) lighter than the Sigma 18-35mm F1.8 DC HSM's weight of 810g.
Filter Threads
The Sigma 18-35mm F1.8 DC HSM has a filter size of 72mm 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 72mm filters that we recommend you to consider for the Sigma 18-35mm F1.8 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 18-35mm F1.8 DC HSM has the Pentax KAF lens mount whereas the Sigma 17-50mm F2.8 EX DC OS HSM has the Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with these mounts are Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III for the Pentax KAF Mount and , and for the Pentax KAF3 Mount.
Sigma 18-35mm F1.8 DC HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Sigma 17-50mm F2.8 EX DC OS HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 18-35mm F1.8 DC HSM has a focal range of 18-35mm and
1.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-52.5mm 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 25.5-75mm when used on a APS-C / DX format camera.