What is the concept of distortion in photography?

When the lens is imaged, the different magnification of the image formed in different areas of the field of view is a kind of distortion, and the closer it is to the edge of the picture, the more serious the distortion is.

Barrel distortion (negative distortion): straight lines except the central cross line in the image bend inward.

Pinch Distortion (Pinch Distortion): The lines in the straight line direction of the image are all bent outward except the reticle in the middle.

Distortion will only lead to image deformation, but will not make the image clear. Theoretically, any lens is distorted, but it is more prominent in a wide-angle lens, which is related to the perspective principle. So the distortion can't be completely eliminated, and only some improvements can be made. If the landlord wants to improve the distortion problem, he can refer to this experience:/album/6Dad5075aE0F41a123E36EF2.html.