The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon 24mm F2.8 STM 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 Canon 24mm F2.8 STM with a length of 23mm, is 67mm shorter. Besides being longer, the Sigma 20mm F1.8 EX DG RF also has a larger diameter of 89mm compared to the Canon 24mm F2.8 STM's 68mm 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. Canon 24mm F2.8 STM weighs 125g, which means it is 395g (75%) lighter than the Sigma 20mm F1.8 EX DG RF which has a weight of 520g.
Filter Threads
The Canon 24mm F2.8 STM has a filter size of 52mm 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 52mm filters that we recommend you to consider for the Canon 24mm F2.8 STM:
And these are the 82mm filters that we recommend for the Sigma 20mm F1.8 EX DG RF:
Lens Mounts
The Canon 24mm F2.8 STM has the Canon EF-S lens mount whereas the Sigma 20mm F1.8 EX DG RF has the Canon EF lens mount. Some of the latest released cameras that are compatible with these mounts are Canon T8i, Canon 90D and Canon SL3 for the Canon EF-S Mount and Canon 1D X III, Canon 6D MII and Canon 5D MIV for the Canon EF Mount.
Sigma 20mm F1.8 EX DG RF is also available in Nikon F (DX) , Pentax KAF, Sony Alpha and Sigma SA mounts.
Focal Range
Canon 24mm F2.8 STM is a prime lens with fixed focal lenght of 24mm which has an effective (full-frame 35mm equivalent) focal range of
38.4mm when used on a APS-C / DX format camera.
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 1.6x crop, it provides a 35mm (FF) equivalent of 32mm.