You asked
Is the samyang af 14mm f 2 8 good on aps c?
Yes, it's a good choice on APS-C. On a Sony E body it frames like 21mm on full frame, and on a Canon RF body like 22mm. The f/2.8 aperture gives about the depth of field of f/4.2 on Sony and f/4.5 on Canon, so you get a bit more in focus than you would at f/2.8 on full frame. It's autofocus, but it isn't stabilised, so keep your shutter speed up. For a wide view on a smaller sensor, these fit well:
If you want to check the maths for other lenses, see Focal length converter.
Written by Claude from this site's pages.