What is anamorphic lens?

Most photography lenses are designed to minimize distortion, except for fisheye lenses. Another exception is the distorted lens.
Unlike fisheye lenses, deformable lenses ensure that straight lines in the image remain straight. However, the distorted lens will horizontally "squeeze" the image. When shooting people, it may make them look "thin", but the actual impression is very strange. This is precisely the imaging characteristic of the deformable lens, not a malfunction! This is also the reason for the emergence of distorted lenses.
In post-processing, by stretching the compressed image, a wider field of view will ultimately be obtained. After stretching the image to restore the correct aspect ratio of the model, the image is now close to a panoramic view.
Unlike the distortion commonly seen in lens evaluations, the "distortion" of distorted lenses is a deliberate result - it helps users shoot with a different aspect ratio than the camera sensor.
Compared with ordinary spherical lenses, the shape of the lens of the deformable lens is slightly different, and its shape is more like a cylinder. Photos taken with a distorted lens must be stretched to obtain a normal aspect ratio. In the era of film, projectors equipped with deformable lenses were able to correct "squeeze" deformations. Nowadays, this correction can be completed using post-processing software.
Different deformable lenses have different compression ratios, such as 1.33 ×, 1.6 ×, or 2 ×. During post-processing, it is necessary to refer to the compression ratio for image stretching.
Transfiguration lenses are usually sold in sets, especially those used for video and movie shooting. The focal length of the lenses in the set is different, but the compression ratio and design/structure are the same.