How many kinds of lenses are there? What are their uses?

Fixed focus lens: A lens with a fixed focal length is called a "fixed focus lens". 1. standard lens (referred to as header): refers to the lens whose focal length is close to or equal to the diagonal length of the film/sensor. For a Quan Huafu 135 SLR camera, the negative width is 24*36mm, and the diagonal length is 50mm, so the focal length of the camera's "head" is 50 mm ... Of course, the focal length of different cameras is different. Generally speaking, the focal length of a 120 camera is 75mm, and that of a 4*5-inch landline is150 mm. The sensor format of a digital SLR camera varies from manufacturer to manufacturer, but as long as the diagonal length of the sensor is calculated, the focal length of a standard lens can be obtained. Although the focal lengths of the "heads" in different frames are different, their visual angles are basically the same, which is close to the normal visual angle of human eyes. Therefore, in terms of framing range and perspective relationship, the "title" is similar to the effect of human eyes, which is particularly cordial and natural. In addition, the technology of the "head" is basically perfect, with the remarkable characteristics of large aperture, outstanding imaging quality and low price, and it is one of the necessary lenses for every SLR user. 2. Wide-angle lens: refers to a lens with a shorter focal length and a larger viewing angle than the "head". For Quan Huafu 135 SLR cameras, the lens with a focal length of about 30mm and a viewing angle of about 70 degrees is called a "wide-angle lens", and the lens with a focal length of less than 22 mm and a viewing angle of more than 90 degrees is called a "super-wide-angle lens". Features of wide-angle lens: A. The depth of field is large, which is conducive to obtaining all clear images. Widely used in the shooting of scenery films. B. The viewing angle is large, and a wider range of framing can be obtained in a limited range, especially the shooting of indoor buildings, which is widely used in the real estate industry. C. strong perspective can create a picture with strong visual impact. D. Distortion is large, especially at the edge of the picture. 3. telephoto lens: refers to a lens with a longer focal length and a smaller viewing angle than the "head". For Quan Huafu 135 SLR cameras, a lens with a focal length of 200mm and a viewing angle of about 12 degrees is called a telephoto lens, and a lens with a focal length of over 300mm and a viewing angle of about 8 degrees is called a super telephoto lens. Features of telephoto lens: A. The depth of field is small, and it is easy to obtain the picture effect with clear subject and blurred background. B. The viewing angle is small, so that a larger picture of the distant subject can be obtained without disturbing the subject. Widely used in outdoor wildlife shooting. C. It compresses the feeling of jumping in perspective and shortens the distance between foreground and background. D. the image distortion is small, and it is widely used in portrait photography. 4. Fisheye lens: an extremely wide-angle lens. For Quan Huafu 135 SLR camera, the lens with focal length below 16mm and viewing angle around 180 degrees can be called "fisheye lens". The characteristics of fisheye lens are as follows: a. The viewing angle is large and the shooting range is extremely wide. B. the sense of perspective is greatly exaggerated. C. The fisheye lens is severely deformed, but it can achieve dramatic effect. D. It is very expensive, originally designed for astrophotography. E. The first lens protrudes outward, so the usual filter cannot be used, and instead it is a "built-in filter". 5. Refractive lens (reflective lens): It is a super telephoto lens, which looks short and fat, with much lighter weight, and is more suitable for hand-held shooting. The lens structure is simple and the imaging quality is excellent. The disadvantage is that there is only one aperture, so it is not convenient to control the depth of field. When the camera takes a view, the view is dark and it is not convenient to focus. At present, most of the catadioptric lenses popular on the market are made in Russia, and their prices are low. Common focal lengths are 500mm and 1000mm, which is one of the good choices for users who are short of money and like telephoto.

Zoom lens: refers to a lens whose focal length can be adjusted freely within a certain range. 1. Types of zoom lenses: a. Manual focusing and autofocus. According to different focusing methods, zoom lenses can be divided into manual zoom lenses and automatic zoom lenses. B. zoom range. Generally speaking, 20-40mm is called wide-angle zoom lens, 35-70mm is called standard zoom lens, 70-200mm is called long-distance zoom lens, and 200-500 is called telephoto zoom lens. Of course, there are also many lenses covering the range from wide angle to medium focus or even telephoto, such as 28-200mm and 28-300mm. C. zoom and enlarge. From the zoom magnification, there are 2 times (such as 35-70mm), 3 times (such as 70-2 10mm), 5 times (28- 135mm), 7 times (28-200mm) and 10 times (50-0 times). Generally speaking, the larger the zoom range, the larger the volume, the lower the image quality and the smaller the aperture. D. zoom mode. According to different operations, it can be divided into push-pull zoom and rotary zoom. The advantage of push-pull zoom is that it is easy to use, and it can quickly zoom from the farthest end to the nearest end. The disadvantage is that the lens is easy to slide when shooting in pitch. The advantage of rotary zoom is that the focus ring and zoom ring are independent, and the rotary operation does not interfere with each other. But the operation is not as simple as push-pull zoom, especially when "zoom shooting explosion effect" is adopted, it is not as easy to realize as push-pull zoom.

Digital lens: a lens designed or improved according to the characteristics of digital SLR cameras. 1. Digital special lens: refers to the lens designed according to the digital sensor of digital SLR camera APS size. This kind of lens can only be used in the corresponding models of digital SLR cameras, and it can't be imaged normally when used in Quan Huafu 135 cameras. A. Several common digital special lenses: Canon EF-S lens, which can only be used on Canon EOS 300D, 350D and 20D digital SLR cameras; Nikon DX lens can be used on all Nikon digital SLR cameras; Olympus digital lens can be used in the digital SLR camera of Olympus 4/3 system; Longtengdi II lens can be used on the digital SLR camera with corresponding bayonet; Tuli DX lens can be used in digital SLR cameras with corresponding bayonet; Sigma DC lens can be used on digital SLR cameras with corresponding bayonet; Minolta DT lens can only be used on Minolta a-7D digital SLR camera; Pentax DA lens: It can be used on Pentax digital SLR cameras. B. Features of digital special lens: Because it is designed for APS size, the volume, weight and price of digital special lens are much lower than those of 135 Quan Huafu lens. For D50 sleeve, on the premise of having AF-S ultrasonic motor, ED lens and aspheric lens, the lens weight is only 2 10g, which is only 2 135 Quan Huafu lens. Improved design of digital sensor: for film, even if the light is obliquely incident, the film can still be fully sensitive; The photosensitive element used in digital camera is a chip with pixels arranged on the grid at regular intervals, and the photodiode is in the groove inside the pixel. Therefore, only when the light enters the lens in a straight line can it reach the photodiode effectively. This means that if a digital SLR is equipped with a 35mm camera lens, it is easy to have inaccurate color reproduction and insufficient brightness at the edge of the photosensitive element where light is incident at an oblique angle, which is generally worse for a wide-angle lens. According to the above characteristics, the special digital lens is improved. For Olympus digital lens, it adopts a brand-new design and optimizes the lens according to the characteristics of photosensitive elements used in digital cameras. The 4/3 system standard and the unique technology of Zuiko digital lens ensure that the light reaches the photosensitive element at a nearly vertical angle, which solves this problem. In this way, a stable and high-quality image can be obtained even at the edge of the image or when using a wide-angle lens. 3. Digitally optimized lens: refers to the lens that has been digitally optimized and improved based on the original 135 Quan Huafu lens and the characteristics of the digital sensor. Usually, this lens can be used in digital SLR cameras or traditional 135 full-frame cameras. At present, digital optimized lenses mainly come from Shima and Longteng in Japan, namely DG lens of Shima and DI lens of Longteng.

Special lens: a lens designed for a special purpose, usually used in professional fields. 1. Macro lens: It is a lens that can be focused very close to the subject, and the size of the image formed by the macro lens on the film or sensor is almost equal to the size of the subject itself. The macro lens marked with 1: 1 means that the image on the film is as big as the subject, the one marked with 1: 2 means that the image on the film is half as big as the subject, and the one marked with 2: 1 means that it is twice as big as the subject. Macro lens is usually a lens with a medium focal length, but it can actually be a lens with any focal length. For example, there are 50mm macro lenses, 180mm macro lenses or 70- 180mm macro zoom lenses. Macro lenses are usually expensive and have excellent picture quality, especially suitable for shooting insects, flowers, stamps, watch parts and other topics. 2. Perspective adjustment lens: a lens with the function of correcting perspective deformation. The main optical axis of the optical system of this lens can be adjusted horizontally or vertically, and the positions of the fuselage and the film or sensor plane do not move during the adjustment. The angle adjusting lens is mainly used for architectural photography. 3. Soft-focus lens: also known as "soft-focus lens" and "soft-light lens", it is a lens that can slightly blur the image, and is mainly used for portrait and landscape photography. 4. Additional lens: A. Extended range lens: the most commonly used additional lens. When in use, it is installed between the camera and the lens, which can increase the focal length of the main lens by a certain magnification. There are 2X and 1.4X, which can increase the focal length by 2 times and 1.4 times respectively. The main disadvantage of using rangefinder is that it reduces the effective aperture of the main lens. Generally speaking, 2X rangefinder reduces 2 apertures. If you shoot normally with the aperture of F 16, you should adjust it to F8 when using the rangefinder. In addition, the consequences of rangefinder include slow autofocus speed and poor image quality. B. Wide-angle additional mirror: The wide-angle additional mirror is installed in front of the main lens for use. Pay attention to the threaded aperture of the main lens when purchasing. Its main function is to reduce the focal length of the main lens. After using the wide-angle additional lens, there is no need for exposure compensation, and the aperture value remains unchanged. However, in order to improve the image quality as much as possible, it is recommended to shoot with a small aperture. Lens structure: 1. Simple lens composed of single or double cemented lenses This simple lens is composed of single or double cemented lenses, so its aberration cannot be perfectly corrected, and its aperture is very small, so it can only be used under strong light. However, due to the extremely low price of such lenses, especially in recent years, optical plastics (PMMA) has been widely used to replace optical glass, which makes its manufacturing cost lower. So at present, most toy cameras and disposable cameras on the market use this simple lens. 2. Three-piece three-group Kirk [[Cook]] lens The early Kirk lens was composed of three independent lenses, and its aperture was located between the lenses. This kind of optical structure is the simplest structure that can preliminarily correct the lens aberration. The imaging quality basically meets the requirements of general public cameras (the lens grade is 2 ~ 3) and the price is relatively low. In recent years, in order to adapt to the development of automatic cameras and pocket cameras, the aperture of the usual three-piece Kirk lens has been moved from the middle of the lens to the back of the mirror to make the lenses closely connected. Due to the asymmetry of optical power caused by the backward movement of the aperture, the system has a large off-axis spherical aberration. In order to ensure the aberration, we have to stop the light, so the edge illumination is relatively low, which needs to be considered in design and use. In order to further reduce the cost, most low-grade parallel cameras on the market now use optical plastics lens to replace one of Kirk's three objective lenses (mostly the middle one), and its relative aperture can only be about 1/4.5. Third, [Tessar] Three groups of four-piece photographic lenses were developed by Kirk lens, originated from 1902 Zeiss Optical Factory in Germany, and were first designed by Rudolof, a famous optical expert. It uses a double cemented lens group to replace the third lens of Kirk lens, so the relative aperture of the lens can be greatly improved, and its relative aperture can reach 1/3.5 ~ 1/2.8 under the condition of medium field of view of 50 ~ 60. At present, it is the most widely used lens structure form for mid-range or mass cameras in China. The aperture is located between the second group and the third group, forming a positive power photographic objective lens with asymmetric structure. The introduced cemented lens group fully improves the astigmatism and off-axis of the objective lens, so it is especially suitable for landscape photography. Fourth, the double Gaussian objective lens and its evolution. The double Gaussian objective is an objective with a relatively large field of view (about 40), and the relative aperture reaches F/2 first. The original design is shown in figure 1-2- 19. Adding two glued surfaces makes it possible to better eliminate aberrations. Although the dispersion of the glass on both sides of the bonding surface is different, the refractive index is almost the same, so the addition of the bonding surface has little effect on the monochromatic aberration. The basic symmetrical structure is conducive to the correction of coma, distortion, magnification chromatic aberration and other vertical aberrations. There are two strong concave lenses on both sides of the aperture, which is conducive to the correction of spherical aberration and astigmatism. The complex type of double Gaussian objective lens mainly increases the relative aperture of the lens or improves the imaging quality of the lens. The most common method is to replace the front or rear positive lens with two single positive lenses, which can reduce the off-axis forward goal difference of the field of view and the on-axis forward goal difference of the aperture at the same time, and obtain higher imaging quality under the condition of larger field of view. Another complex form of double Gaussian objective lens is to replace the adhesive surface in the front and rear thick lenses with the separation surface; Or split the front or rear positive lens into two at the same time. According to the structure, the lens can also be divided into many kinds, which can be explained in detail here (from Wuji): /showthread.php? threadid=2223 13