How to solve the attenuation of picture quality by the characteristics of the shift lens


1) Perspective control

   Shift lens mimics the characteristics of large-format technology cameras that can move up and down, and many mainstream manufacturers’ product lines include at least No less than one shift lens. The photographer uses the feature of shifting axis to change the focal plane, control the depth of field, and can also correct the convergence of vertical lines when shooting buildings. The focal length of the most commonly seen shift lens is 45 mm.

   Usually the deformation of the subject is unacceptable, especially architectural photographers, they will try to correct this problem. Advertising and landscape photographers can also take advantage of the characteristics of the shift lens to shoot unique images.

  2) Tilt

   The tilt function of the lens allows the photographer to tilt the clear focal plane to make this plane No longer perpendicular to the optical axis of the lens. This will produce a depth-of-field effect in the shape of a wedge, with the width changing with distance. Therefore, tilt does not really increase the depth of field, it only allows the photographer to adjust the position to better express the subject.

   Through the control of the lens tilt, even if the subject plane is parallel to the imaging plane, you can get a part of the clear and part of the blurred image, while the ordinary lens can only shoot All clear images are obtained, and even by adjusting the angle between the subject plane and the imaging plane, the effect of extremely shallow depth of field can be obtained.

  3) Offset

   When the subject plane and the imaging plane are parallel to the lens design, any subject The parallel lines of will remain parallel on the final image. However, if the imaging plane is not parallel to the plane of the subject, such as looking up and shooting a tall building, the parallel lines will have a converging effect and the subject will appear unnatural. The lens shift function can keep the focal plane parallel to the subject plane, so that the convergence effect of this parallel line can be corrected.

   Normally, this kind of design is mainly used in architectural photography to prevent perspective distortion on both sides of the building. The shift lens can also be shifted in the opposite direction, so that this convergence of parallel lines can be deliberately exaggerated.

  The image circle of a shift lens is larger than that of a lens with the same focal length. The image circle of the ordinary lens is close to the four corners of the picture, while the image circle of the shift lens is much larger. In this way, it can be ensured that the image sensor is in the imaging circle even when the axis is shifted. When the shift lens is not tilted and shifted, the optical performance will not decrease due to the use of the central part of the large image circle, and it has the same high optical performance as the fixed focus lens.

   Most of the high-definition cameras we use now use CMOS chips, and the illuminance performance can only reach 0.5Lux. When the focal length of a telephoto lens changes, the luminous flux will also change. The longer the focal length, the worse the luminous flux. When the focal length is extended to the maximum, the luminous flux is reduced to the weakest. Although it is daytime, for the camera optical lens camera, it is equivalent to being blocked in front, leaving only a small hole to transmit light. In this case, ordinary high-definition cameras will suffer from image degradation due to insufficient illumination. To solve this problem, you can start from two aspects:

   1. Use high-definition cameras designed for remote monitoring, such as Hitachi’s latest KP-HD1005 high-definition SDI camera. In addition to achieving a minimum illumination of 0.3Lux, this camera has also added technology for color reproduction and low illumination image enhancement for the field of long-distance monitoring. Makes a clear picture even when the luminous flux drops.

  2, increase the luminous flux of the lens when the focal length is elongated. Once the lens is produced, the range of luminous flux is determined and cannot be changed. Therefore, when choosing a lens, we must choose products with long focal lengths with better light flux performance. According to the optical relationship of the lens, F (the inverse ratio of luminous flux) u003d f (focal length)/D (the effective aperture in front of the lens). The F value is inversely proportional to the luminous flux. The smaller the value, the better the luminous flux performance. Then in the case of the same f, choose a lens with a larger effective aperture, the better the picture effect will be. KOWA's lens design adopts a large-caliber design. For example, the newly designed 750mm 2 million-pixel high-definition lens uses a 104mm super-large front effective aperture. In similar products, it can provide the camera with more excellent light performance.

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