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The key to the design of the lens in the high-definition era and the use of the shift lens
In the era of high definition, the industry's requirements for lenses are getting higher and higher. In line with the development of the times, the industry is constantly improving new designs and manufacturing processes to meet application requirements in different fields. Analyze several key issues about lens design in the high-definition era for you.
One, the lens adopts ED lens is the key
The commonly used surveillance market, we use more fixed Focus or manual zoom lens, because the monitoring distance is relatively short, the focal length of the lens generally used is within 50mm. This kind of scene has almost no requirement for the anti-dispersion performance of the lens.
But once a motorized zoom lens is used to monitor distant targets, the chromatic dispersion problem becomes prominent (the chromatic dispersion is that the light of various wavelengths in the visible light will be refracted by the lens. There is a focus shift, which is manifested in the image that there is a blue or red color bar at the edge of the object).
Originally, in the analog surveillance system, due to the large pixel size, the problem of dispersion is not very prominent, and it will only show up when the focal length is above 300mm. In the high-definition era, this problem can be clearly seen in the commonly used electric zoom lens with a focal length of 120mm. This puts higher requirements on the lens in terms of material and coating accuracy.
The higher the definition of the matched camera, the more obvious the influence of lens material on the imaging effect. For example, KOWA's high-definition electric zoom lens uses a large number of ED lenses in the lens design. It can provide a clear picture effect for the camera during long-distance monitoring at a long focal length.
Second, the large-aperture design is the key
Then can the lens with ED lens be able to completely solve the long distance? What about the monitoring problem? Usually, we turn the output image with a resolution above 720p into a high-definition image. According to the free choice of the market, the output format of 1080p is mostly adopted. In the field of long-distance monitoring, users hope to use high-definition monitoring systems to increase the pixels of the picture, and then to watch remote targets more clearly.
According to our actual experience, using a high-definition system to watch, not only does not make the picture sharpness commission, but the color reproduction ability and sharpness of the picture are greatly attenuated, and the output image is clear The image quality is worse than D1, and even worse than analog cameras. When the focal length is lengthened, the picture becomes a black and white picture, the sharpness is severely reduced, and the image effect is worse than the effect of the same lens with a Hitachi ultra-low illumination camera.
It’s not difficult to understand that this situation occurs. 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, the optical lens is equivalent to being blocked in front of the camera, leaving only a small hole for light to pass through. In this case, ordinary high-definition cameras will suffer from picture quality degradation due to insufficient illumination.
The purpose of the shift lens:
The function of the shift lens was originally used to correct the normal wide-angle lens to take pictures The perspective problems that occurred at the time, but later they were widely used to create photographic works with varying depth of focus positions. The shift lens is mainly used for architectural photography and advertising photography.
The optical axis of a conventional lens is fixed and it is perpendicular to the image sensor plane (focal plane). Therefore, if you tilt the camera up or down, the subject will be deformed. This kind of deformation is manifested as vertical lines converging to the inside, which is most common when shooting buildings, for example. The root cause of this deformation is that the focal plane of the camera is not parallel to the plane of the subject. Shift lenses, also known as perspective control lenses, are designed to correct this problem. In the field of architectural photography, the shift lens is a necessity, and in other photography fields, the shift lens also has its uses.
Axis shift lens can make the optical axis perform two kinds of movement: tilt and offset. Tilt can change the direction of the focal plane, so that a part of the image is clear, while the rest is out of focus. Offset is to move the lens along the direction parallel to the focal plane, which is used to correct perspective and eliminate the convergence problem of parallel lines.