Classification of lens distortion

Pinch distortion, also known as pincushion distortion, is a phenomenon that the picture shrinks to the middle caused by the lens. When we use telephoto lens or telephoto end of zoom lens, the pincushion distortion is most easily detected. Especially after using the focal length converter, pincushion distortion is easy to occur. When there are straight lines in the picture (especially those near the edge of the picture), the pincushion distortion is most easily detected. The pincushion distortion rate of ordinary consumer digital cameras is usually 0.4%, which is lower than the barrel distortion rate. The opposite of pincushion distortion is barrel distortion.

Processing method: You can use the middle part of the lens to deform the picture with smaller resolution, leaving more margin, and then PS cropping.

It can also be corrected by software. Barrel distortion, also known as barrel distortion, is a barrel distortion phenomenon caused by the physical properties of the lenses in the lens and the structure of the lens group. When we use a wide-angle lens or the wide-angle end of a zoom lens, we are most likely to detect barrel distortion. Barrel distortion is most easily detected when there are straight lines in the picture (especially those near the edge of the picture frame). The barrel distortion rate of ordinary consumer digital cameras is usually 1%. The opposite of barrel distortion is pincushion distortion.

Distortion is caused by the large inclination angle of light. Unlike spherical aberration and astigmatism, distortion does not destroy the concentricity of the beam, so it does not affect the clarity of the image. Distortion is manifested in the fact that each part of the character in the image plane is out of proportion to the original. Distortion is related to the position of the diaphragm.

Generally, wide-angle lenses have more or less barrel distortion, especially at the wide-angle end of zoom lenses. Due to the cost, many large zoom cameras have more congenital defects than portable cameras.

Solution: It can be corrected by software. For example, there is a plug-in called Panorama Tool in PS, which can effectively correct the distortion. Linear distortion, also known as linear distortion.

When trying to photograph tall linear structures, such as buildings or trees, it will lead to another kind of distortion. Suppose you use a wide-angle lens, thinking that as long as you aim the camera up a little, you can get close and photograph the whole structure. However, because parallel lines are actually uneven, the result is that buildings or trees seem to fall down. This distortion phenomenon is called linear distortion.

The problem is that the camera is tilted upwards, and the direction in which the camera is aimed causes the two sides of a building or tree to be like a typical railway track, that is, they converge towards the center, resulting in normal depth perspective.

If the photographer is standing in a static position in the middle of a wall or a tree of a building, then the perspective relationship above is not unnatural. However, when the photographer's position deviates from the center, the problem arises because the two sides of the structure do not converge at the same angle. For example, there is a wall of a building, one side looks straight up and down, and the other side looks 30, so the photo taken looks like a pyramid instead of a skyscraper.

This kind of problem does not only appear on wide-angle lenses, but any lens will produce linear distortion if the shooting angles are the same. It's just that the wide-angle lens makes the line tilt more obvious, which makes this phenomenon more obvious.

How to solve this problem? Actually, it's very simple. Just make the back of the camera parallel to the front of the building being photographed. If you can't shoot the whole building, either change the wide-angle lens or shoot it backwards.

Another way to solve the linear distortion problem is to install a camera on the back of the machine. This camera can move the lens up and down or left and right, so that the front of the subject is parallel to the film at a fixed position. This is why architectural photographers almost always use the lens behind the lens.