>>4027862>>4027867>>4027870>>4027874>>4027875it's not perspective distortion like the other guy said, it's barrel distortion
every lens at focal length less than 50mm will have barrel distortion, even slightly because the field of view is larger than the actual size of the lens
using a 50mm equivalent crop will not help, try cropping a fisheye lens to a 50mm fov and you'll see that it's still distorted. this is an extreme example but it holds true for all wide angle lenses
