The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Panasonic S 18mm F1.8 and the Sigma 20mm F1.8 EX DG RF 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 20mm F1.8 EX DG RF is the longer of the two lenses at 90mm. The Panasonic S 18mm F1.8 with a length of 82mm, is 8mm shorter. Besides being longer, the Sigma 20mm F1.8 EX DG RF also has a larger diameter of 89mm compared to the Panasonic S 18mm F1.8'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. Panasonic S 18mm F1.8 weighs 340g, which means it is 180g (34%) lighter than the Sigma 20mm F1.8 EX DG RF which has a weight of 520g.
Filter Threads
The Panasonic S 18mm F1.8 has a filter size of 67mm whereas the Sigma 20mm F1.8 EX DG RF has a 82mm 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 Panasonic S 18mm F1.8:
And these are the 82mm filters that we recommend for the Sigma 20mm F1.8 EX DG RF:
Lens Mounts
The Panasonic S 18mm F1.8 has the Leica L lens mount whereas the Sigma 20mm F1.8 EX DG RF has the Sony Alpha lens mount. Some of the latest released cameras that are compatible with these mounts are Leica SL3, Panasonic S5 II and Panasonic S5 II X for the Leica L Mount and Sony A99 II, Sony A68 and Sony A77 II for the Sony Alpha Mount.
Sigma 20mm F1.8 EX DG RF is also available in Canon EF , Nikon F (DX), Pentax KAF and Sigma SA mounts.
Focal Range
Panasonic S 18mm F1.8 is a prime lens with fixed focal lenght of 18mm.
On the other hand, the Sigma 20mm F1.8 EX DG RF is a prime lens with fixed focal lenght of 20mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 30mm.