The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-300 F3.5-6.3 DC OS HSM and the Sigma 50-500mm F4.5-6.3 DG OS HSM for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Sigma 50-500mm F4.5-6.3 DG OS HSM is the longer of the two lenses at 219mm. The Sigma 18-300 F3.5-6.3 DC OS HSM with a length of 102mm, is 117mm shorter. Besides being longer, the Sigma 50-500mm F4.5-6.3 DG OS HSM also has a larger diameter of 104mm compared to the Sigma 18-300 F3.5-6.3 DC OS HSM's 79mm diameter.
The 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 18-300 F3.5-6.3 DC OS HSM weighs 585g, which means it is 1385g (70%) lighter than the Sigma 50-500mm F4.5-6.3 DG OS HSM which has a weight of 1970g.
Below you can find the dimension and weight table of the SuperZoom Lenses in Sony Alpha Mount for size comparison purposes.
SuperZoom Lenses in Sony Alpha Mount for Size Comparison
Lens Mounts
Both the Sigma 18-300 F3.5-6.3 DC OS HSM and the Sigma 50-500mm F4.5-6.3 DG 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 A68, Sony A77 II and Sony A58.
Sigma 18-300 F3.5-6.3 DC OS HSM is also available in Canon EF , Nikon F (DX), Pentax KAF3 and Sigma SA mounts.
Sigma 50-500mm F4.5-6.3 DG OS HSM is also available in Canon EF , Pentax KAF3, Sigma SA and Nikon F (FX) mounts.
Focal Range
Sigma 18-300 F3.5-6.3 DC OS HSM has a focal range of 18-300mm and 16.7X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-450mm when used on a APS-C / DX format camera. Sigma 50-500mm F4.5-6.3 DG OS HSM has a focal range of 50-500mm and 10.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 75 - 750mm.