Tilt-shift lens, what is a tilt-shift lens?

Generally, when taking pictures of buildings, you stand on the ground. In order to take a full picture, the camera needs to be tilted upward slightly. Since the lower part of the building is closer and the upper part is further away, it will produce a convergence effect of "larger at the bottom and smaller at the top". The lens itself is not deformed. The reason for this phenomenon is due to the perspective relationship. Correction: The camera is facing the building. At this time, the angle of view of the lens may be insufficient and you need to change to a wider-angle lens. For a 35mm camera, the equivalent method is to use a lens of the same focal length but with a larger angle of view, shoot directly at the target, and move the film to the position you want to retain when cutting (actually panning the lens in the opposite direction). This kind of lens is a "tilt-shift lens", and the principle is as mentioned above. Tilt-shift lens works A lens that moves the optical axis of the lens to adjust the perspective. The function of a tilt-shift lens is not only to correct perspective distortion, but also to adjust the position of the focal plane. Under normal circumstances, the focal plane of the camera is parallel to the film plane. When shooting with a large aperture, the scene on the focal plane will be clear and the out-of-focus scene will be blurry. If you use a tilt-shift lens to adjust the focal plane, the sharp point can be changed. Obviously, tilt-shift lenses are best for architectural, landscape, and commercial photography. EF tilt-shift lenses do not have AF function. This kind of lens is designed to be movable because it has a special device that can move or tilt. Its focal length is generally 28mm or 35mm. Tilt-shift lenses can be used to correct perspective problems. When your location when shooting is much closer to the bottom of the building than to the top of the building, the following situation will occur. The entire building seems to be compressed, and the roofs are also gathered together, giving the effect that the building is about to fall down. If you change to a tilt-shift lens, you can avoid this situation. Tilt-shift lenses can eliminate perspective distortion because when shooting tall buildings, the lens needs to be tilted up in order to capture a panoramic view. As a result, there is a certain angle between the plane of the film and the main line of the tall building, and the upper part becomes smaller due to the farther distance between the objects, causing perspective distortion. After the tilt-shift lens is moved, the center of the lens does not pass through the center of the film, so the distance between the upper and lower parts of the film to the center of the lens is not equal. Although the object distance of the upper part is farther, the corresponding image distance of the lower part is also farther, and the corresponding change in magnification offsets the perspective Distortion, as long as the film plane is parallel to the main line of the building, the photos taken will have no perspective distortion. It is equivalent to shooting with a large-format camera (such as a 120 camera) with a lens of the same focal length (wider angle) and then cropping it to a 135 frame. If we shoot with an ultra-wide-angle lens and then crop and zoom in, the effect is the same as a tilt-shift lens, but the resolution cannot be fully utilized. Depth of field control in tilt-shift lens works not only requires the lens to have a tilt-shift function, but also requires the lens to have a swing function, such as Canon's TS-E lens. From the picture, you can see that there is an arc and scale, and there is a flat surface near the rotating axis, which all serve the rotation function. The combination of tilt shift and oscillation can focus an inclined plane onto the focal plane, thereby making objects on the inclined plane clear. This is not possible with ordinary lenses. Ordinary lenses can only focus clearly on a plane perpendicular to the central axis of the lens. These functions of the tilt-shift lens are only available on large landline cameras. Realizing these functions not only requires a complex mechanical structure, but also requires the lens to have a larger field of view and a larger rear working space, so tilt-shift lenses are very expensive. Due to the special mechanical structure, tilt-shift lenses generally do not have automatic aperture. Tilt-shift lenses are mainly used for architectural photography, and their uses are relatively specialized. Therefore, there are only a few 135 tilt-shift lenses, and there are also relatively few DX and films in this area. After searching in Wuji, there were occasional discussions, but they were also very old.