The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sony 24-70mm F2.8 ZA SSM and the Sigma 18-50mm F2.8-4.5 DC OS HSM for their suitability to various photography scenarios:
Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Sony 24-70mm F2.8 ZA SSM is the longer of the two lenses at 111mm. The Sigma 18-50mm F2.8-4.5 DC OS HSM with a length of 89mm is 22mm shorter. Besides being longer, the Sony 24-70mm F2.8 ZA SSM also has a larger diameter of 83mm compared to Sigma 18-50mm F2.8-4.5 DC OS HSM's 74mm 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 18-50mm F2.8-4.5 DC OS HSM weighs 395g, 58% (560g) lighter than the Sony 24-70mm F2.8 ZA SSM's weight of 955g.
Below you can find the dimension and weight table of the 'Standard Zoom Lenses in Sony Alpha Mount for size comparison purposes.
Standard Zoom Lenses in Sony Alpha Mount for Size Comparison
Both Sony 24-70mm F2.8 ZA SSM and Sigma 18-50mm F2.8-4.5 DC OS HSM 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.
Sigma 18-50mm F2.8-4.5 DC OS HSM is also available in Canon EF , Pentax KAF3, Sigma SA and Nikon F (DX) mounts.
Sony 24-70mm F2.8 ZA SSM 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.
Sigma 18-50mm F2.8-4.5 DC OS HSM has a focal range of 18-50mm and 2.8X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-75mm when used on a APS-C / DX format camera.