The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-300 F3.5-6.3 DC OS HSM and the Tamron 28-300mm f3.5-6.3 VC PZD 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 18-300 F3.5-6.3 DC OS HSM is the longer of the two lenses at 102mm. The Tamron 28-300mm f3.5-6.3 VC PZD with a length of 96mm, is 6mm shorter. Besides being longer, the Sigma 18-300 F3.5-6.3 DC OS HSM also has a larger diameter of 79mm compared to the Tamron 28-300mm f3.5-6.3 VC PZD'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 28-300mm f3.5-6.3 VC PZD weighs 540g, 7% (45g) lighter than the Sigma 18-300 F3.5-6.3 DC OS HSM's weight of 585g.
Filter Threads
The Sigma 18-300 F3.5-6.3 DC OS HSM has a filter size of 72mm whereas the Tamron 28-300mm f3.5-6.3 VC PZD has a 67mm 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 18-300 F3.5-6.3 DC OS HSM:
And these are the 67mm filters that we recommend for the Tamron 28-300mm f3.5-6.3 VC PZD:
Lens Mounts
The Sigma 18-300 F3.5-6.3 DC OS HSM has the Sigma SA lens mount whereas the Tamron 28-300mm f3.5-6.3 VC PZD has the Sony Alpha lens mount. Some of the latest released cameras that are compatible with these mounts are Sigma SD1 Merrill, Sigma SD1 and for the Sigma SA Mount and Sony A99 II, Sony A68 and Sony A77 II for the Sony Alpha Mount.
Sigma 18-300 F3.5-6.3 DC OS HSM is also available in Canon EF , Nikon F (DX), Pentax KAF3 and Sony Alpha mounts.
Tamron 28-300mm f3.5-6.3 VC PZD is also available in Canon EF and Nikon F (FX) mounts.
Focal Range
Sigma 18-300 F3.5-6.3 DC OS HSM has a focal range of 18-300mm and
16.7X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-450mm when used on a APS-C / DX format camera.
On the other hand, the Tamron 28-300mm f3.5-6.3 VC PZD has a focal range of 28-300mm and 10.7X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 42 - 450mm.