The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 120-400mm F4.5-5.6 DG OS HSM and the OM System 12-40mm F2.8 PRO 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 120-400mm F4.5-5.6 DG OS HSM is the longer of the two lenses at 203mm. The OM System 12-40mm F2.8 PRO II with a length of 84mm, is 119mm shorter. Besides being longer, the Sigma 120-400mm F4.5-5.6 DG OS HSM also has a larger diameter of 92mm compared to the OM System 12-40mm F2.8 PRO II's 70mm 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. OM System 12-40mm F2.8 PRO II weighs 382g, 76% (1258g) lighter than the Sigma 120-400mm F4.5-5.6 DG OS HSM's weight of 1640g.
Filter Threads
The Sigma 120-400mm F4.5-5.6 DG OS HSM has a filter size of 77mm whereas the OM System 12-40mm F2.8 PRO II has a 62mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 77mm filters that we recommend you to consider for the Sigma 120-400mm F4.5-5.6 DG OS HSM:
And these are the 62mm filters that we recommend for the OM System 12-40mm F2.8 PRO II:
Lens Mounts
The Sigma 120-400mm F4.5-5.6 DG OS HSM has the Sigma SA lens mount whereas the OM System 12-40mm F2.8 PRO II has the Micro Four Thirds lens mount. Some of the latest released cameras that are compatible with these mounts are Sigma Quattro, Sigma Quattro H and Sigma SD1 Merrill for the Sigma SA Mount and OM System OM-3 Astro, OM System OM-5 II and OM System OM-3 for the Micro Four Thirds Mount.
Sigma 120-400mm F4.5-5.6 DG OS HSM is also available in the Canon EF and Nikon F (FX) mounts.
Focal Range
Sigma 120-400mm F4.5-5.6 DG OS HSM has a focal range of 120-400mm and
3.3X zoom ratio .
On the other hand, the OM System 12-40mm F2.8 PRO II has a focal range of 12-40mm and 3.3X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 24-80mm when used on a FourThirds format camera.
