You asked

Sigma 17 40mm f 1 8 dc art vs tamron 16 50mm f 2 8 a?

Here is what the site says about that.

From Sigma 17-40mm f/1.8 DC Art: Sigma 17-40mm f/1.8 DC Art: A zoom lens by Sigma for APS-C cameras, 17-40mm f/1.8. A constant f/1.8 standard zoom for APS-C mirrorless, in the spirit of the 18-35mm f/1.8 for DSLRs. Specs - Maker: Sigma - Focal length: 17-40mm (zoom) - Maximum aperture: f/1.8 - Made for: APS-C sensors - Mounts: Sony E, Fujifilm X, L-Mount, Canon RF - Stabilised: no - Autofocus: yes What it frames like - On APS-C (Sony E, Fujifilm ...

From Tamron 16-50mm f/2.8 A: Tamron 16-50mm f/2.8 A: A zoom lens by Tamron for APS-C cameras, 16-50mm f/2.8. A 305-gram constant f/2.8 standard zoom for APS-C mirrorless bodies. Specs - Maker: Tamron - Focal length: 16-50mm (zoom) - Maximum aperture: f/2.8 - Made for: APS-C sensors - Mounts: Sony E, Nikon Z, Fujifilm X, Canon RF - Stabilised: no - Autofocus: yes What it frames like - On APS-C (Sony E, Nikon Z, Fujifilm X): like 24-75mm on ...

Quoted from this site's pages.

From these pages