What is a digital camera equivalent focal length

Digital camera lens focal length is always to 135 camera lens as a reference, the main reason is because the popularity of 135 camera, the most widespread introduction of it also the most, its understanding was also the most. The camera lens is the lens shooting range is an important parameter, a different focal length lens fit different photography needs. Fixed focal length lens General Division of the digital camera lens focal length is always to 135 camera lens as a reference, the main reason is because the popularity of 135 camera, the most widespread introduction of it also the most, its understanding was also the most. The camera lens is the lens shooting range is an important parameter, a different focal length lens fit different photography needs. Fixed focal length lens generally consists of a wide angle lens, standard lens and telephoto lens. Standard lens refers to focal length approximately equal to the photosensitive surface (negatives, CCD or CMOS) diagonal length of the lens. The "look" (shooting) object's perspective and from the perspective of the eyes (of course not the glimmer of the human eye is also taken into account) is very similar. On 135 camera, the emulsion size 36 × 24mm, diagonal length of 43mm. Thus the focal length of lens around 43mm is the standard lens, it is customary to get around the lens to 50mm standard lens. On the site of the camera in the 120, the emulsion dimensions: 45 x 60mm, 60 × 90 × 60mm 60mm and, therefore, its standard lens focal length range from 75 ~ 110mm. Focal length is less than the standard lens that wide angle lens, but larger than the standard lens called the telephoto lens. 50mm standard lens perspective (emulsion diagonal endpoints to the lens center line the angle) 47 degrees, wide-angle lens angle of view than standard lens, to take a wider scope, telephoto lens angle of view than standard lens for small, shooting range is also small. A simple rule is that the greater the angle, focal distance, focal length, the greater the smaller the angle of view. Digital cameras due to its emulsion (CCD or CMOS) size is varies with the camera (135 camera emulsion is fixed). Only to the true focal length camera lens is difficult to compare different camera shooting range, are converted to the equivalent of 135 camera lens focal length before comparison. To date, in addition to the Canon, Kodak DCS 14n EOS-1Ds and Contax N DIGITAL III camera and 135 camera has the same photosensitive area, but the others are little more than 135 camera, so these three camera lens focal length and 135 of the camera lens is no different. Conversion lens is divided into two categories, one category is for emulsion size aspect ratio is 3: 2, and 135 camera photographic surface proportions the same digital camera. This kind of camera are SLR interchangeable lens camera (apart from Canon EOS 300D, basically is a professional camera). The other type is for photosensitive surface dimensions of aspect ratio of 4: 3, and computer monitor screen aspect ratio for the same digital camera. These cameras are mostly civilian camera (there are very few SLR professional cameras are, such as Olympus E-1). On the first class of digital camera, although they all use 135 camera lens, but the angle of view is not the same. How to put their lens conversion into equivalent focal length? is based on the diagonal angle of view of both must be equal. Set f equivalent lens focal length (unit: mm), f1 is a true digital camera lens focal length (unit: mm), d1 is digital camera emulsion diagonal length (unit: mm), similar to the nature of the triangle is not difficult to get screen.width-80) {this.width = screen.width-80; this.alt = ' this picture has been reduced, click here to view the original size of the picture. ';}" Border = "0" alt = ""/> i.e. screen.width-80) {this.width = screen.width-80; this.alt = ' this picture has been reduced, click here to view the original size of the picture. ';}" Border = "0" alt = ""/> which screen.width-80) {this.width = screen.width-80; this.alt = ' this picture has been reduced, click here to view the original size of the picture. ';}" Border = "0" alt = ""/> called lens factor