Sigma 17mm f/4 DG Contemporary

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Prime lens

A prime lens by Sigma for Full frame cameras, 17mm f/4. A tiny metal ultra-wide from the I series; sold as the 17mm f/4 DG DN before 2025.

What it frames like

Its full-frame-equivalent focal length on the sensor it was made for.

How wide 17mm sees on each sensor it covers.

f/4 wide open, to scale against f/1.4.

On full frame (Sony E, L-Mount): as marked, 17mm.
On APS-C (Sony E, L-Mount): like 26mm on full frame; f/4 gives about the depth of field of f/6 there.