The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 17-50mm f2.8 XR II LD and the Sigma 17-70mm F2.8-4 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 17-70mm F2.8-4 DC OS HSM is the longer of the two lenses at 89mm. The Tamron 17-50mm f2.8 XR II LD with a length of 82mm, is 7mm shorter. Besides being longer, the Sigma 17-70mm F2.8-4 DC OS HSM also has a larger diameter of 79mm compared to the Tamron 17-50mm f2.8 XR II LD'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. Tamron 17-50mm f2.8 XR II LD weighs 430g, which means it is 90g (17%) lighter than the Sigma 17-70mm F2.8-4 DC OS HSM which has a weight of 520g.
Filter Threads
The Tamron 17-50mm f2.8 XR II LD has a filter size of 67mm whereas the Sigma 17-70mm F2.8-4 DC OS HSM 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 Tamron 17-50mm f2.8 XR II LD:
And these are the 72mm filters that we recommend for the Sigma 17-70mm F2.8-4 DC OS HSM:
Lens Mounts
The Tamron 17-50mm f2.8 XR II LD has the Pentax KAF lens mount whereas the Sigma 17-70mm F2.8-4 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 Mono, Pentax KF and Pentax K-3 III for the Pentax KAF Mount and , and for the Pentax KAF3 Mount.
Tamron 17-50mm f2.8 XR II LD is also available in the Canon EF , Nikon F (DX) and Sony Alpha mounts.
Sigma 17-70mm F2.8-4 DC OS HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Tamron 17-50mm f2.8 XR II LD 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.
On the other hand, the Sigma 17-70mm F2.8-4 DC OS HSM has a focal range of 17-70mm and 4.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 25.5-105mm when used on a APS-C / DX format camera.
