Standard lens classification and common camera lens terminology
Standard lenses can be divided into standard zoom lenses and standard fixed focus lenses.
1) Standard zoom lens
Standard zoom lens has greatly exceeded the traditional 50mm fixed focus in practicality Lens. Most of the new digital SLR camera kit lenses are standard zoom lenses, and the most common focal lengths are 28-70 mm and 50 mm. This general focal length range is very suitable for everyday photography.
2) Standard fixed focus lens
The traditional 50mm standard fixed focus lens may seem somewhat outdated, but It is actually a very useful lens. It is very close to the perspective of the human eye, so that it is convenient to truly restore the subject. Standard lenses usually have a large maximum aperture, are light and compact, and have high optical quality.
Standard lens concept:
The standard lens used in traditional SLR cameras is 50mm, in fact, the focal length is about 50mm The lens is usually regarded as a standard lens. The standard lens has an angle of view and perspective similar to that of the human eye, and its focal length is approximately equal to the length of the diagonal of the image sensor.
It is undeniable that the standard lens is somewhat underestimated today. Many photographers think that the focal length of a standard lens is very close to that of the human eye, and the angle of view is too ordinary and nothing new. In fact, standard lenses should not be ignored at all. They can be said to be excellent shooting tools that we can use daily in lens design and are suitable for various shooting themes. This focal length can be very suitable for all kinds of subjects, including scenery, still life and snapshots.
Common camera lens terms
can also be called negative distortion, which is an imaging defect. The image point of the barrel-shaped deformed image will shift as the distance from the center point increases. The middle section of the 'straight line' in the image bends outwards, and the two ends bend toward the center to become 'curves'. Therefore, the image of a square object will become four corners shrinking inward, and the middle section of the sideline will bulge outward, like a wooden barrel, so it is called barrel deformation.
Generally, as the angle of view of the lens expands (that is, the focal length decreases), the barrel deformation becomes more and more serious. Specifically, the image captured by a wide-angle lens is most often barrel-shaped. The picture below is a photo taken with a 24mm wide-angle lens. It is obvious that the edges of the photo are curved inward.
Moreover, if you shoot with a fisheye lens, the image will become even more circular.
Although barrel deformation is an imaging defect, if used properly, it can take very special photos. It depends on the photographer's creativity and the experience of using the lens! Optical lens
2) Chromatic Aberration
The camera lens uses white light to form an image, while white light It is composed of various visible light of different wavelengths. Although the same electromagnetic waves, visible light of different wavelengths (colors) will have different speeds when passing through the glass, so there are so-called different refractive indexes. Using this principle, we can decompose white light into light of different colors (wavelengths) as long as we use a diamond mirror.
The camera lens is made of glass, and uses the principle of refraction to focus visible light into an image. After the light passes through the lens, there is a chance that a rhombohedral mirror-like effect appears. Lights of different wavelengths cannot be focused at the same focal point, and dispersion is formed on the image, which is the so-called purple fringing phenomenon. You can use the following figure to understand how the chromatic aberration of the lens creates a dispersion image at the center and edge of the image.