The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 16-300mm f3.5-6.3 II VC PZD and the Sigma 18-125mm F3.8-5.6 DC 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. Tamron 16-300mm f3.5-6.3 II VC PZD is the longer of the two lenses at 100mm. The Sigma 18-125mm F3.8-5.6 DC HSM with a length of 89mm, is 11mm shorter. Besides being longer, the Tamron 16-300mm f3.5-6.3 II VC PZD also has a larger diameter of 75mm 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, 9% (50g) lighter than the Tamron 16-300mm f3.5-6.3 II VC PZD's weight of 540g.
Filter Threads
The Tamron 16-300mm f3.5-6.3 II VC PZD has a filter size of 67mm whereas the Sigma 18-125mm F3.8-5.6 DC HSM has a 62mm 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 16-300mm f3.5-6.3 II VC PZD:
And these are the 62mm filters that we recommend for the Sigma 18-125mm F3.8-5.6 DC HSM:
Lens Mounts
Both the Tamron 16-300mm f3.5-6.3 II VC PZD and the Sigma 18-125mm F3.8-5.6 DC HSM has the same Sony Alpha lens mount. Some of the latest released cameras that are compatible with the Sony Alpha lenses are Sony A68, Sony A77 II and Sony A58.
Tamron 16-300mm f3.5-6.3 II VC PZD is also available in Canon EF and Nikon F (DX) mounts.
Sigma 18-125mm F3.8-5.6 DC HSM is also available in Pentax KAF3 mount.
Focal Range
Tamron 16-300mm f3.5-6.3 II VC PZD has a focal range of 16-300mm and
18.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
24-450mm when used on a APS-C / DX format camera.
On the other hand, the 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.