The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-50mm F2.8-4.5 DC OS HSM and the Sony DT 18-55mm F3.5-5.6 SAM II 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 18-50mm F2.8-4.5 DC OS HSM is the longer of the two lenses at 89mm. The Sony DT 18-55mm F3.5-5.6 SAM II with a length of 69mm, is 20mm shorter. Besides being longer, the Sigma 18-50mm F2.8-4.5 DC OS HSM also has a larger diameter of 74mm compared to the Sony DT 18-55mm F3.5-5.6 SAM II's 72mm 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. Sony DT 18-55mm F3.5-5.6 SAM II weighs 222g, 43% (173g) lighter than the Sigma 18-50mm F2.8-4.5 DC OS HSM's weight of 395g.
Below you can find the dimension and weight table of the Standard Zoom Lenses in Sony Alpha Mount for size comparison purposes.
Standard Lenses in Sony Alpha Mount for Size Comparison
Filter Threads
The Sigma 18-50mm F2.8-4.5 DC OS HSM has a filter size of 67mm whereas the Sony DT 18-55mm F3.5-5.6 SAM II has a 55mm 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 Sigma 18-50mm F2.8-4.5 DC OS HSM:
And these are the 55mm filters that we recommend for the Sony DT 18-55mm F3.5-5.6 SAM II:
Lens Mounts
Both the Sigma 18-50mm F2.8-4.5 DC OS HSM and the Sony DT 18-55mm F3.5-5.6 SAM II 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.
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.
Focal Range
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.
On the other hand, the Sony DT 18-55mm F3.5-5.6 SAM II has a focal range of 18-55mm and 3.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-82.5mm when used on a APS-C / DX format camera.