What kinds of SLR lenses are generally classified by focal length?

There are many ways to classify photographic lenses, but they are usually classified as follows:

(l) According to the focal length or field angle of the lens, the lens can be divided into three categories: standard lens, short focal length (wide angle) lens and telephoto lens.

When general cameras are sold, most of them are equipped with standard lenses.

The focal length of the standard lens is basically equal to the diagonal length of the negative frame. Although there are still differences in the field of view (generally between 45 and 55), most of them are close to the human eye's perspective.

Therefore, the perspective relationship of pictures taken with standard lens is more in line with people's visual habits.

Due to the moderate focal length, field of view, shooting range and depth of field of the standard lens, and the image size obtained at the same shooting distance, this lens is the most widely used and is most suitable for taking pictures of portraits, landscapes, life and so on.

A wide-angle lens is a short-focus lens.

According to the length of the focal length, there are wide-angle and ultra-wide-angle lenses.

Characterized in that:

Short focal length, large field of view and wide shooting range.

When the distance cannot be increased in a narrow environment, the wide-angle lens can expand the shooting field of vision and take photos of panoramic or large scenes within a limited distance.

The wide-angle lens also has the characteristics of super-scale rendering, which exaggerates the prospect.

In photography, we can make full use of the special perspective created by it to exaggerate the depth of the scene and highlight the main part.

The wide-angle lens has short focal length and long depth of field, and the photos taken are very clear.

Therefore, it is suitable for capturing some activities that are too late to focus calmly, and it is more suitable for taking news photos of big scenes or photos of indoor family life.

Wide-angle lens is an indispensable photographic lens in landscape photography because of its large wishing angle and wide depth of field. At present, ordinary plastic automatic cameras on the market are equipped with wide-angle lenses.

Medium focal length lens belongs to long focal length lens. The focal length of a medium focal length lens is about twice that of a standard lens, and the focal length of a long focal length lens is longer.

Its * * * features are:

Long focal length, small field of view angle and large negative imaging.

Therefore, at the same distance, you can take larger images than the standard lens. It is suitable for photographing the activities of distant people or animals, and shooting some inaccessible objects to get natural and vivid pictures.

Because the range of depth of field of the medium-long focal length lens is smaller than that of the standard lens, it is beneficial to blur the background of the subject, and the subject is generally far away from the camera, which has less deformation in the perspective of the portrait or the main scene and will make the portrait more vivid. Therefore, people often call the medium focus lens a portrait lens.

Ordinary civilian users rarely use telephoto lenses, because the lens barrel of telephoto lenses is long and heavy, relatively expensive, and the depth of field is relatively small, so it is difficult to focus in practical use, so it is often used for professional photography.

(2) The lens can be divided into super-transparent lenses according to its condensing ability, and the relative aperture of the photographic objective should be above 1:2.8; Strong light transmission lens,1:3.5 ~1:5.8; Normal transparent lens,1:6.3 ~1:9; Weak light transmission lens, less than 1:9.

(3) According to whether the focal length of the lens can be changed, it can be divided into fixed-focus lens and zoom lens.

Due to the rapid improvement of optical design level and optical glass melting technology, it is possible for wealthy photographers to choose an optical system whose focal length can be changed within a certain range while keeping the image surface fixed.

This kind of camera lens, which can change the focal length value in a certain range, so as to obtain different field of view angles, different images and different scene ranges, is called zoom photographic objective lens, or zoom lens for short. Zoom lens can change the shooting range by changing the focal length without changing the shooting distance, so it is very beneficial to picture composition.

Because a zoom lens can also serve as several fixed-focus lenses, it not only reduces the number of photographic equipment to carry when traveling, but also saves the time for changing lenses. At present, almost all the top automatic fool cameras produced abroad are equipped with zoom lenses with small zoom ratio.

Zoom lenses can be divided into single ring and double ring according to different zoom methods. Single-ring zoom lens, zoom and focus with the same pull ring, push and pull it to zoom and rotate it to focus; Its advantages are simple and quick operation.

Double-ring zoom lens, one of which is used for zooming and focusing respectively; The advantages are that zooming and focusing do not interfere with each other, and the accuracy is high, but the operation is more troublesome. At present, some zoom lenses on the market are marked with the word "micro" on the front ring of the lens, which means that they can be used for macro photography or ultra-close photography, so such zoom lenses are more widely used.

However, due to its complex optical system and mechanical structure, zoom lens is difficult to manufacture and is restricted by price, volume and weight.

It is impossible to make the relative aperture of the zoom lens very large. Sometimes, in order to reduce the volume or ensure aberration, the lens can only change the aperture.