The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 50-500mm F4.5-6.3 DG OS HSM and the Sigma 18-250mm F3.5-6.3 DC 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 18-250mm F3.5-6.3 DC OS HSM with a length of 101mm, is 118mm 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 18-250mm 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 18-250mm F3.5-6.3 DC OS HSM weighs 628g, 68% (1342g) lighter than the Sigma 50-500mm F4.5-6.3 DG OS HSM's weight of 1970g.
Below you can find the dimension and weight table of the SuperZoom Lenses in Sigma SA Mount for size comparison purposes.
SuperZoom Lenses in Sigma SA Mount for Size Comparison
Lens Mounts
Both the Sigma 50-500mm F4.5-6.3 DG OS HSM and the Sigma 18-250mm F3.5-6.3 DC OS HSM has the same Sigma SA lens mount. Some of the latest released cameras that are compatible with the Sigma SA lenses are Sigma Quattro, Sigma Quattro H and Sigma SD1 Merrill.
Sigma 50-500mm F4.5-6.3 DG OS HSM is also available in Canon EF , Pentax KAF3, Sony Alpha and Nikon F (FX) mounts.
Sigma 18-250mm F3.5-6.3 DC OS HSM is also available in Canon EF , Nikon F (DX), Pentax KAF3, Sony Alpha, Sigma SA, Canon EF, Nikon F (DX), Pentax KAF3 and Sony Alpha mounts.
Focal Range
Sigma 50-500mm F4.5-6.3 DG OS HSM has a focal range of 50-500mm and 10.0X zoom ratio . Sigma 18-250mm F3.5-6.3 DC OS HSM has a focal range of 18-250mm and 13.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-375mm when used on a APS-C / DX format camera.