What does the focal length parameter of SLR camera lens mean?

Numbers represent focal length, 18 represents wide-angle end, and 105 represents telephoto end. In short, the objects photographed from 18mm to 105mm are gradually enlarged, and correspondingly, the field of vision is gradually reduced.

It can be understood as the optical amplification of DC. 18-55mm is a zoom lens, which means the focal length will change, and 35mm is a fixed-focus lens. The image quality of zoom is not as good as that of fixed focus, but the zoom lens is easy to use and can be adjusted at any time. Both fixed-focus and zoom lenses have their own advantages and uses. 35mm is mostly used for documentary photography, and 55mm is mostly used for portraits.

Of course, this is not absolute, each focal segment has its own imaging characteristics, and you will naturally understand if you shoot more.

Parameters:

When the focal length is smaller than the pan/tilt, the lens can record images with a larger angle of view, so it is called a wide-angle lens. The perspective of a wide-angle lens is exaggerated. Under the wide-angle lens, the closer you are, the smaller you are, especially in landscape photography, you can take more photos with visual impact.

A lens whose focal length is 1.5 ~ 4 times larger than that of the meter head is called medium focus. Generally, the medium focus lens has the smallest deformation, and it is relatively easy to design it into a super-large aperture, so portrait photography is what the medium focus lens is best at. Generally, the focal length of the title is 1.5 ~ 2 times, which is used to take photos of the whole body and chest circumference. Shots larger than 2 times are mostly used for close-ups, and several shots called "portrait king" in the shot all appear in this focal part.

A lens that is more than twice the focal length of the head is called a telescope head. As the name implies, the telescopic lens can achieve "telescopic" shooting, which is mostly used to shoot sports, animals and so on. The application of telescope lens in scenery film can compress the far and near perspective of the scene.

Standard lens: For 135 camera, the lens with a focal length of about 50MM-the viewing angle is about 43 degrees. The perspective effect of photos taken by standard lens is similar to that of human eyes, which is extremely natural and not exaggerated.

Documentary photos can faithfully record what they see by using the title, so most documentary photographers like to use the title, such as French photographer Bresson.

The focal length of the standard lens of cameras with different film sizes is different, because the definition of the focal length of the standard lens is that the focal length is equal to the diagonal length of the negative. For 35mm film, that is, film used by 135 camera, the focal length of standard lens is 50 mm. ..

Other large format cameras, such as 120 camera, use 6X6 film, and the focal length of its standard lens should be about 90 mm. Other large format cameras can also calculate the focal length of its standard lens.

Wide-angle lens: a lens with a focal length of less than 35MM-when the focal length is smaller than that of the pan/tilt, the lens can record images with a larger angle of view, so it is called a wide-angle lens. The perspective of wide-angle lens is exaggerated, showing obvious perspective effect and emphasizing the sense of distance. It is widely used in news photography and landscape photography and will have a strong visual impact.

Medium focus lens: a lens with a focal length of 85 mm ~ 135 mm-a lens with a focal length of 1.5 ~ 4 times the focal length of the head is generally called medium focus. The photo taken at this focal length has the smallest deformation, can correctly reflect the shape of the subject, and it is relatively easy to design it into a super-large aperture. In portrait photography, medium focus is the most commonly used.

Telescope head: a lens with a focal length of more than 200MM-it has a small sense of distance and can compress the perspective of the landscape.

Extended data:

Detailed description of lens recognition

AI: automatic maximum aperture transfer technology. Published in 1977, used for manual lens. Logo does not appear in the lens name, and the smallest number on the aperture ring of AI lens is green.

AI-S: automatic shutter index transfer technology. Published in 198 1 for manual lens. There is no logo in the lens name, and the smallest number on the aperture ring of AI-S lens is yellow.

AF: autofocus technology. The AF in the name indicates that this is an autofocus lens, but the lens itself has no motor. If the body does not have a focus motor, it cannot focus automatically.

AF-I: 1992 lens has built-in motor and CPU contacts, which are mainly used for professional telephoto lenses. Has been replaced by af-S.

AF-S: autofocus lens with built-in SWM ultrasonic motor. This kind of lens can also achieve autofocus on low-end cameras such as Nikon D5 100/D3 100 without a body motor.

ASP: Indicates that an aspherical lens is used in the lens.

CRC: short-range error correction system. The system enables photographers to obtain excellent image quality when shooting at close range and increasing the focus range.

D: focal length data transmission technology. D-lens supports 3D matrix photometry.

DC: defocused image control. Nikon original lens can provide unique zoom control function. Its main feature is that it allows fuzzy control of the foreground or background of a specific object to obtain better defocus imaging.

DX: Special lens for APS-C camera, with small image field design, can't be used on Quan Huafu fuselage.

Ed: That means ultra-low dispersion lenses are used in the lens.

G: G lens cancels the traditional manual aperture ring. G lens often appears on Nikon's latest lens together with AF-S, showing an upgrading trend.

Macro: Macro lens.

N: It was once used to represent a new lens, but now the N with a hexagonal bottom on the lens means that the lens is coated with nanocrystals.

PC-Shift: move the lens.

Radio frequency: rear group focusing technology.

S: Thin, appearing on some thin lenses.

SIC: super composite coating.

TC: rangefinder.

VR: image anti-shake system. This shows that the lens has anti-shake function.

References:

Baidu encyclopedia-teaching section