The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 85mm F1.8 VC and the Sigma 70mm F2.8 EX DG Macro 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 70mm F2.8 EX DG Macro is the longer of the two lenses at 95mm. The Tamron 85mm F1.8 VC with a length of 91mm is 4mm shorter. On the other hand, the Tamron 85mm F1.8 VC has a larger diameter of 85mm compared to Sigma 70mm F2.8 EX DG Macro's 76mm 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. Sigma 70mm F2.8 EX DG Macro weighs 527g, 24% (173g) lighter than the Tamron 85mm F1.8 VC's weight of 700g.
Lens Mounts
Both Tamron 85mm F1.8 VC and Sigma 70mm F2.8 EX DG Macro has the same Sony Alpha lens mount. Some of the latest released cameras that are compatible with the Sony Alpha lenses are Sony A99 II, Sony A68 and Sony A77 II.
Tamron 85mm F1.8 VC is also available in Canon EF and Nikon F (FX) mounts.
Sigma 70mm F2.8 EX DG Macro is also available in Canon EF , Nikon F (FX), Pentax KAF and Sigma SA mounts.
Focal Range
Tamron 85mm F1.8 VC is a prime lens with fixed focal lenght of 85mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 127.5mm.
Sigma 70mm F2.8 EX DG Macro is a prime lens with fixed focal lenght of 70mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides an 35mm (FF) equivalent of 105mm.