What are the characteristics of optical lenses

Optical lens is an important part of TV camera, which is generally composed of multiple convex and concave lenses combined with corresponding metal parts. Nowadays, the general camera lens is equipped with automatic iris, electric zoom and other devices. The optical lens is the  of the camera, and its basic function is to image the subject on the photosensitive element in the camera. The optical characteristics of a lens refer to the physical properties formed by its optical structure, consisting of three factors: focal length, field of view, and relative aperture. Any kind of optical lens can be represented and distinguished by the technical parameters of these three optical characteristics. For TV filmmakers, the focal length of the lens, the angle of view, and the relative aperture will all have an impact on the picture shooting. Their technical performance and composition The matching relationship directly determines the technical and artistic possibilities that the photographer can achieve. 1. Focal length The camera lens can be regarded as a convex lens with a thick middle and a thin edge. The light passes through the lens and condenses into a focal point. The distance from the focal point to the center of the lens is the focal length of the lens. The unit of focal length is millimeter (mm). The length of the focal length of the lens is proportional to the imaging area of ​​the charge-coupled device (CCD) of the subject. If you shoot the same subject at the same distance, the longer the focal length of the lens. Then the larger the imaging area, the higher the magnification; on the contrary, the shorter the focal length of the lens, the smaller the imaging area and the lower the magnification. Generally, we call a lens whose focal length is close to or equal to the diagonal of the image plane as a standard lens. The imaging area of ​​the charge-coupled device of a general professional camera is approximately equal to the image plane of a 16 millimetre water movie camera. The focal length of a standard lens is usually 25 millimeters. A lens with a focal length greater than the diagonal of the image plane is called a long focal length lens, and a lens with a focal length smaller than the diagonal of the image plane is called a wide-angle lens. A lens whose focal length can be changed is called a zoom lens. 2. Field of view The field of view angle of the lens refers to the angle formed by the edge of the effective imaging plane (field of view) of the charge-coupled device and the node behind the lens. From the modeling point of view, the field of view of the lens reflects the openness of the camera's recorded scene range (the field of view of the lens is divided into the horizontal field of view and the vertical field of view. The field of view used in this chapter refers to the horizontal field of view). The field of view of the lens is inversely proportional to the imaging effect of the subject in the picture. The larger the field of view, the smaller the image of the subject and the wider the scene; on the contrary, the smaller the field of view, the larger the image of the subject. , The narrower the field of view of the scene. The angle of view is mainly restricted by the two factors of lens imaging size and lens focal length. Since the imaging target surface of the camera tube is a constant factor in actual shooting, the focal length of the lens directly affects the angle of view. When we shoot, generally we can only change the angle of view by changing lenses with different focal lengths. When the camera is shooting the same subject at the same distance, using lenses with different focal lengths will change the imaging area and background range of the subject in the screen. This is essentially due to the corresponding change in the angle of view. For example, a subject captured by a lens with a field of view of 50° has only 1/10 of the area of ​​the image captured by a lens with a field of view of 5°. The longer the focal length of the lens, the smaller the angle of view; the shorter the focal length, the larger the angle of view. Normally, the standard lens (25mm lens) we call has a focal length approximately equal to the diagonal length of the imaging face and a horizontal field of view of about 45°; for the zoom lens on the camera, it is the lens with a focal length of about 25mm. The horizontal field of view of the wide-angle lens (focal length less than 25mm) is greater than 60°, and one is between 60°-130°. A lens between 130° and 180° is called an ultra-wide-angle lens, also called a fisheye lens. The horizontal field of view of a long focal length lens (focal length greater than 25mm) is less than 40°.