The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 45mm F1.8 Di VC USD and the Sigma 18-50mm F2.8-4.5 DC OS HSM 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. Tamron 45mm F1.8 Di VC USD is the longer of the two lenses at 92mm. The Sigma 18-50mm F2.8-4.5 DC OS HSM with a length of 89mm, is 3mm shorter. Besides being longer, the Tamron 45mm F1.8 Di VC USD also has a larger diameter of 80mm compared to the Sigma 18-50mm F2.8-4.5 DC OS HSM'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. Sigma 18-50mm F2.8-4.5 DC OS HSM weighs 395g, 24% (125g) lighter than the Tamron 45mm F1.8 Di VC USD's weight of 520g.
Filter Threads
Both the Tamron 45mm F1.8 Di VC USD and the Sigma 18-50mm F2.8-4.5 DC OS HSM have the same Filter thread size of 67mm.
Below are links to the 67mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Tamron 45mm F1.8 Di VC USD and the 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.
Tamron 45mm F1.8 Di VC USD is also available in the Canon EF and Nikon F (FX) mounts.
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
Tamron 45mm F1.8 Di VC USD is a prime lens with fixed focal lenght of 45mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
67.5mm.
On the other hand, the 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.
