========================[Concept]The photographic lens focal length longer than the standard size.Refers to the longer focal length, perspective is less than the "header" of the lens.Generally higher than 135mm above the lens is a telephoto lens, also known as a telephoto lens.Among them, more than 300mm above the telephoto lens.========================[Sub class]Full-size 135-SLR(1) the focal length 200mm, the lens of the angle at 12 degrees or so called "telephoto lens"2 the focal length of 300mm above the angle at 8 degrees around the lens is called the "super-telephoto lens.========================[Features]----------------(1) short depth of field]Easy access to the main clear picture bokeh effect. Can make in your subject be highlighted in a cluttered environment.But some difficulties for precise focusing, focus when shooting a little inaccurate, it will cause the main virtual paste.----------------(2) [perspective]Larger the distance the main screen and does not interfere with the subject. Widely used in outdoor wildlife shooting.Range of shooting the scene space, in the same shooting distance, the image taken is greater than the standard lens for shooting distant scenery detail and shooting is not easy closeThe subject.----------------3 Perspective poorThis lens has compressed space depth distance and exaggerated rear view features.----------------(4) the lens focal length, camera we must grasp the more stable, in order to avoid image blur.Inspection criteria is that only when the shutter speed at least equal to the lens focal length in millimeters countdown when the hand-held lens to shoot, also known as "safety shutter.In other words, when the shutter speed below 1/100 seconds can not be armed with 100mm lens, less than 1/500 sec can not be armed with a 500mm lens shooting.For most of the telephoto lens, shooting are required to use a tripod, so you not only to carry the bird long shot, but also carrying a tripod.----------------Compression of the sense of the perspective of the screen jump closer to the distance of the foreground and background.========================[Use]Telephoto lens perspective, weak sense of perspective scenery deformation, suitable for shooting inaccessible things, such as wildlife, the stage, you can also use a telephoto lens to blur the background of portraits.Are generally used to shooting distant scenery.Due to air absorption and diffuse scattering of light. Therefore, the contrast of images taken smaller, combined with dust extinction more serious, is not easy to achieve very precise focusing.More than 300 mm super-telephoto lens is also difficult to colored light at one point, resulting in sub-spectrum problem.Based on the above, sometimes the image quality of the work taken is not high.========================[Excellent point]Long-range shooting scenery figures, travel photography, portrait photography (in the shooting of the standard photo posted documents, the ordinary application of about 100 mm telephoto lens shooting, in order to reduce the shadowSuch as distortion, with 105 mm lens, the best)2 stage, sporting events and other photos taken in the stands, shooting animals in the zoo, shooting animals in the wild, plus auxiliary mirror shoot close-ups ... and so on,========================[Use]Using a long focal length lens shooting, the general application of fast photographic film and fast shutter speeds, such as the use of 200 mm focal length lens, the shutter speed should be more than 1/250 seconds, to prevent camera shake when shooting hand-held camera images of virtual paste.Under normal circumstances, shooting, in order to maintain the stability of the camera, the best camera fixed on a tripod.3 super-telephoto lenses are generally only in exceptional circumstances only use, the use of feed can not just use ordinary fixed camera tripod, otherwise, the lens will be overweight broke the camera on a tripod base.Therefore, the need to use a kind of tripod supporting the lens holder fixed camera, this particular tripod can be used to fix the two three-legged, a fixed camera body, a fixed support super-telephoto lenses. The best use of fast the ISO400/27 film, to ensure that there is sufficient shutter speed.========================[Note]----------------(1) the use of high-speed shutterThe telephoto lens is bulky, heavy and difficult to securely grip when shooting.Another telephoto lens imaging magnification, subject movement or camera shake a little blurring of the image corresponding increase, and therefore must use a higher shutter speed.Different focal length telephoto lens with the shutter speed should be higher than the reciprocal of the value of the lens focal length, so as to avoid camera shake, image blur, such as using a telephoto lens focal length 200 mm, shutter speed 1 / more than 250 seconds.----------------(2) selection of high-speed sensitive film]Due to the smaller diameter telephoto lens, holding machine in order to prevent instability, often need to use a high shutter speed shooting with ISO100 speed sensitive film is difficult to meet the needs of high-speed shutter, the exposure, so armed with a long focal length lens when shooting good selection of high-speed film.----------------3 [due to increased exposure]This mainly refers to more than 200mm telephoto lens, its focal length, length mirror lens piece, and has reduced the intensity of the light reaches the film, should increase the exposure to compensate for light loss.Where the focal length of 200-400mm lens to increase the half-level of exposure, focal length above 400mm ultra-telephoto lens to increase the exposure level.TTL metering, the camera is not included.----------------4 plus filter]Telephoto lens to shoot Vision is easy to produce the phenomenon of gray, the scene is not clear and translucent.This is due to UV interference, as well as dust and air medium reflex caused by low image contrast, fuzzy boundaries, poor definition, shot with a telephoto lens vision are advised to install the polarizer, UV filter to eliminate ultraviolet and reflective effects, to improve photo contrast and sharpness.----------------(5) a solid tripod]Telephoto lens photography with the help of a tripod has three advantages:First, use a solid tripod with the shutter cord to release the shutter, and can effectively prevent the faint vibration of the camera, ensure negatives Results like clear;Second, it helps the camera uses a slower shutter speed and small aperture in order to overcome the disadvantage of smaller depth of field of a telephoto lens;Third, can more accurately focus the viewfinder. Long focal length lens depth of field is very small, especially in close-up shots, depth of field is often only a few millimeters in a very short moment it is necessary to framing but also focus, but also to steady the camera, is not easy, a tripod can provide you with help.========================

【Article is excerpted from: Baidu Encyclopedia】【Network reprint / Just reference】【Translation is by Goolge】