The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron AF 28-80mm f3.5-5.6 and the Sigma 24-70mm F2.8 EX DG for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Sigma 24-70mm F2.8 EX DG is the longer of the two lenses at 116mm. The Tamron AF 28-80mm f3.5-5.6 with a length of 70mm is 46mm shorter. Besides being longer, the Sigma 24-70mm F2.8 EX DG also has a larger diameter of 89mm compared to Tamron AF 28-80mm f3.5-5.6's 72mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Tamron AF 28-80mm f3.5-5.6 weighs 237g, which means it is 478g (66%) lighter than the Sigma 24-70mm F2.8 EX DG which has a weight of 715g.
Below you can find the dimension and weight table of the 'Standard Zoom Lenses in Pentax KAF Mount for size comparison purposes.
Standard Zoom Lenses in Pentax KAF Mount for Size Comparison
Lens Mounts
Both Tamron AF 28-80mm f3.5-5.6 and Sigma 24-70mm F2.8 EX DG has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax KF, Pentax K-3 III and Pentax K-1 II.
Tamron AF 28-80mm f3.5-5.6 is also available in Canon EF , Nikon F (FX) and Sony Alpha mounts.
Sigma 24-70mm F2.8 EX DG is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (FX) mounts.
Focal Range
Tamron AF 28-80mm f3.5-5.6 has a focal range of 28-80mm and 2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 42 - 120mm.
Sigma 24-70mm F2.8 EX DG has a focal range of 24-70mm and 2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 36 - 105mm.