You asked
What is the tamron 17 50mm f 4 di iii vxd good for?
The Tamron 17-50mm f/4 Di III VXD is a light, everyday standard zoom for Sony E mount. It starts at 17mm, so it covers wide scenes, street, and general walking-around shots. The constant f/4 keeps the size down, though it won't give you the low-light reach of a faster lens. It has autofocus but no image stabilisation, so use it with a steady hand or a faster shutter speed.
On full frame it's exactly 17-50mm. On APS-C, it frames like 26-75mm, which makes it a handy kit lens for bodies like the Sony a6400 or Sony a6700. On a full-frame body such as the Sony a7 IV, it's a sensible first zoom.
If you want a fast prime to pair with it, see your first lenses.
Written by Claude from this site's pages.