Why does a shift-axis lens have a large aperture effect?

Generally speaking, the axis-shifting lens is used to shoot buildings, which makes use of its own characteristics. You can choose the focal plane by adjusting the lens, so that there will be no distortion when shooting buildings. Nowadays, many photographers also use this feature to shoot other subjects, so they can choose the focal plane they want to shoot at will and highlight the subjects they want to shoot. Of course, there is no contradiction between the large aperture and the shift axis. The aperture of the shift axis lens is also relatively large, but the focal plane has changed, and the depth of field control is more arbitrary, so that things that are not in the focal plane will be blurred and obvious. This feature is illusory, and many of them are like models, which are different from what our eyes see, so many photographers use it to create images.

With the explanation of shifting lens in encyclopedia, you can search more, which is introduced in many professional photography forums.

Tilt shift lens

Nikon shift lens usually shoots buildings standing on the ground. In order to take a complete picture, the camera should be tilted slightly upward. Because the lower part of the building is close to the upper part and far from the upper part, the convergence effect of "the lower part is big and the upper part is small" will be adopted. The lens itself is not deformed, and the reason for this phenomenon is the perspective relationship. Correction: The camera is shooting a building. At this time, the lens angle may be insufficient, and it is necessary to change a lens with a wider angle. At the same time, a large area of the ground will be photographed at the lower part of the picture, and the effective picture is very small, resulting in film waste and reduced resolution. If you use a large-format camera with the same focal length, shoot directly at the target and then cut out the desired picture, you can solve this problem. For a 35mm camera, the equivalent method is to shoot directly at the target with a lens with the same focal length but a larger viewing angle, and move the film to the reserved position when cutting (actually, the lens translates in the opposite direction). This kind of lens is the "axis-shifting lens", and the principle is as mentioned above.

A lens that moves the optical axis to adjust the viewing angle. The function of the shift lens is not only to correct the perspective deformation, but also to adjust the focal plane position. In general, the focal plane of the camera is parallel to the film plane, and the scene in the focal plane is clear and the Jiao Wai is blurred when shooting with large aperture; If the focal plane is adjusted by moving the axis lens, the sharpness can be changed. Obviously, shifting lens is most suitable for architecture, landscape and commercial photography. EF shift lens has no AF function.

This kind of lens is designed to be movable because it has a special device that can move or tilt, and the focal length is generally 28mm or 35 mm

Shift-axis lens can be used to correct perspective problems. When you take a photo, the location is much closer to the bottom of the building than to the top of the building, and the following will happen. The whole building image is compressed, and the roofs are also gathered together, which will cause the building to collapse. This situation can be avoided if a shift lens is used.

Shift-axis lens can eliminate perspective distortion, because when shooting tall buildings, the lens needs to be tilted upward to get a panoramic view. Results The film plane is at a certain angle with the main line of the high-rise building, and the upper part becomes smaller due to the long distance between objects, resulting in perspective deformation. After the axis-shifting lens moves, 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 upper object distance is far, the corresponding image distance of the lower part is also far, and the corresponding magnification change offsets the perspective deformation. As long as the film plane is parallel to the main line of the building, there is no perspective deformation in the photos taken. It is equivalent to shooting with a large camera (such as 120 camera) with the same focal length lens (wider angle) and then cropping to 135 frames. If we shoot with a super wide-angle lens and then enlarge it, the effect is the same as that of a shift-axis lens, but the resolution cannot be fully utilized.

Depth of field control not only requires the lens to have the function of shifting axis, but also requires the lens to have the function of swinging, such as Canon TS-E lens. As can be seen from the figure, there is an arc and scale, and there is a small plane near the axis of rotation, all of which serve the rotation function. By shifting the axis and swinging, an inclined plane can be focused on the focal plane, so that the object on the inclined plane can be imaged clearly. This can't be done on a normal lens. Ordinary lenses can only focus clearly on the plane perpendicular to the lens axis. These functions of the axis shift lens are only available in large landlines. To achieve these functions, not only complex mechanical structure is needed, but also the lens has a larger field of vision and a larger rear working space, so the axis-shifting lens is very expensive. Due to the special mechanical structure, the axis-shifting lens generally has no automatic aperture.

Axis-shifting lens is mainly used in architectural photography, and its use is more specialized, so there are few axis-shifting lenses in 135, and there are also few DX and film in this respect. It was a long time ago that I searched in Wuji and occasionally discussed it. I hope that architectural photographers and the owners of 135 shift lenses can communicate more, and give more advice here, mainly posting more.