The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 100-400mm F5-6.3 DG OS HSM and the Sigma 120-400mm F4.5-5.6 DG 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. Sigma 120-400mm F4.5-5.6 DG OS HSM is the longer of the two lenses at 203mm. The Sigma 100-400mm F5-6.3 DG OS HSM with a length of 182mm, is 21mm 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 Sigma 100-400mm F5-6.3 DG OS HSM's 86mm 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 100-400mm F5-6.3 DG OS HSM weighs 1160g, which means it is 480g (29%) lighter than the Sigma 120-400mm F4.5-5.6 DG OS HSM which has a weight of 1640g.
Below you can find the dimension and weight table of the Telephoto Zoom Lenses in Sigma SA Mount for size comparison purposes.
Super Telephoto Lenses in Sigma SA Mount for Size Comparison
Filter Threads
The Sigma 100-400mm F5-6.3 DG OS HSM has a filter size of 67mm whereas the Sigma 120-400mm F4.5-5.6 DG OS HSM has a 77mm 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 100-400mm F5-6.3 DG OS HSM:
And these are the 77mm filters that we recommend for the Sigma 120-400mm F4.5-5.6 DG OS HSM:
Lens Mounts
Both the Sigma 100-400mm F5-6.3 DG OS HSM and the Sigma 120-400mm F4.5-5.6 DG 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 100-400mm F5-6.3 DG OS HSM is also available in Nikon F (FX) and Canon EF mounts.
Sigma 120-400mm F4.5-5.6 DG OS HSM is also available in Canon EF and Nikon F (FX) mounts.
Focal Range
Sigma 100-400mm F5-6.3 DG OS HSM has a focal range of 100-400mm and
4.0X zoom ratio .
On the other hand, the Sigma 120-400mm F4.5-5.6 DG OS HSM has a focal range of 120-400mm and 3.3X zoom ratio .