Sigma 10-18mm f/2.8 DC DN Contemporary (Fuji X) vs Voigtlander NOKTON 35mm f/1.2 Aspherical (Fuji X)

These cover different focal lengths — the Sigma 10-18mm f/2.8 DC DN Contemporary (Fuji X) is 10-18mm, the Voigtlander NOKTON 35mm f/1.2 Aspherical (Fuji X) is 35mm — so they're not really substitutes. Pick by the field of view you actually need: the Sigma 10-18mm f/2.8 DC DN Contemporary (Fuji X) for wide-angle, the Voigtlander NOKTON 35mm f/1.2 Aspherical (Fuji X) for short-telephoto / portrait.

Choose the Sigma 10-18mm f/2.8 DC DN Contemporary (Fuji X) if you shoot wide — it starts at 10mm vs 35mm for landscapes, interiors and architecture. Choose it if you want one-lens flexibility — a 10-18mm zoom covers what the fixed 35mm can't reframe. Choose it if you like close-focus work — 0.28x magnification vs 0.13x. Choose it if you work outdoors — it's weather-sealed against dust and moisture; the other isn't.

Choose the Voigtlander NOKTON 35mm f/1.2 Aspherical (Fuji X) if you want more light and background blur — f/1.2 is faster than f/2.8, better for low light and subject separation. Choose it if you need more reach — it goes to 35mm vs 18mm for distant subjects, wildlife and sport. Choose it if you prefer a fast, compact single focal length — a 35mm prime over a zoom.

Aperture: the Voigtlander NOKTON 35mm f/1.2 Aspherical (Fuji X) opens to f/1.2 vs the Sigma 10-18mm f/2.8 DC DN Contemporary (Fuji X)'s f/2.8 — more light and shallower depth-of-field.