Canon RF 24mm f/1.8 Macro IS STM vs Sigma 10-18mm f/2.8 DC DN Contemporary (Canon RF)

These cover different focal lengths — the Canon RF 24mm f/1.8 Macro IS STM is 24mm, the Sigma 10-18mm f/2.8 DC DN Contemporary (Canon RF) is 10-18mm — so they're not really substitutes. Pick by the field of view you actually need: the Canon RF 24mm f/1.8 Macro IS STM for standard, the Sigma 10-18mm f/2.8 DC DN Contemporary (Canon RF) for wide-angle.

Choose the Canon RF 24mm f/1.8 Macro IS STM if you want more light and background blur — f/1.8 is faster than f/2.8, better for low light and subject separation. Choose it if you need more reach — it goes to 24mm vs 18mm for distant subjects, wildlife and sport. Choose it if you prefer a fast, compact single focal length — a 24mm prime over a zoom. Choose it if you shoot handheld or on an unstabilised body — it has optical stabilisation, the other doesn't.

Choose the Sigma 10-18mm f/2.8 DC DN Contemporary (Canon RF) if you shoot wide — it starts at 10mm vs 24mm for landscapes, interiors and architecture. Choose it if you want one-lens flexibility — a 10-18mm zoom covers what the fixed 24mm can't reframe.

Aperture: the Canon RF 24mm f/1.8 Macro IS STM opens to f/1.8 vs the Sigma 10-18mm f/2.8 DC DN Contemporary (Canon RF)'s f/2.8 — more light and shallower depth-of-field.