You asked
What is the sigma 24mm f 3 5 dg contemporary good for?
The Sigma 24mm f/3.5 DG Contemporary is a small, pocketable wide prime, so it suits travel, street, and environmental portraits, where you want to keep the scene around your subject. On full frame it gives a true 24mm view. It's a good choice if you carry a camera all day and don't want a heavy lens. It has no stabilisation, so you'll rely on the camera's own system or a steady shutter speed.
It fits Sony E and L-Mount bodies. Full-frame options include the Sony a7 III and the Panasonic Lumix S5. If you shoot APS-C, the Sony a6400 is a sensible pairing, though on that body the lens frames like 36mm.
For more on how focal lengths work across formats, see the lenses guide.
Written by Claude from this site's pages.