Focusing on the optical axis of the lens, many people like to take pictures in life, which is very easy for professionals. There are many shots you may not know, and many people may not know much about them. So, let's look at the optical axis of the fixed-focus lens.
Fixed focus lens optical axis 1 fixed focus lens can be classified in many ways.
Taking 1 as an example, it can be divided into refractive type and reflective type according to the way of optical path travel. Most fixed-focus lenses are refractive lenses, and the light changes direction through the lens to focus on the imaging element. The reflective lens is mainly a folding lens, and the light will first reflect back and forth through the mirror, and then focus on imaging.
2. According to the lens, it can be divided into fixed optical axis lens and adjustable optical axis lens. For example, ordinary fixed focus; Folding lenses belong to fixed optical axis lenses. There is a kind of lens called shift axis lens, which is a lens with adjustable optical axis. You can change the perspective deformation relationship and adjust the depth of field.
3. Among the most common fixed-focus lenses, they can also be divided into wide-angle lenses10 ~ 35mm according to the focal length; Standard lens 50mm；; Medium focal length lens 55 ~105 mm; Telephoto lens135 ~ 300mm; The ultra telephoto lens exceeds 300 mm
4, according to the purpose, you can have a scenery lens; Humanistic documentary lens; Portrait lens; Wild photographic lens; Macro lens.
5. According to the function pricing, it is divided into "dog head"; Tauren; "manual head"; "automatic head"; "shake your head"; "red circle head"; "golden round head"; "original factory director"; "Deputy Director" and so on. ...
6. According to the instrument system, it can be divided into 135 SLR lens; Paraxial lens; Medium format lens; Large format lens.
The optical axis 2 of the fixed-focus lens magnifies manual focusing, and if it can be clear, it is out of focus.
Optical axis deviation is generally caused by violent collision of lenses. Of course, some cheap lenses use plastic lens barrels, which will also cause optical axis deviation due to wear and deformation after long-term use. But it doesn't mean that the new lens will be fine. There are so many lenses in a lens, even if one lens is installed by a few tenths of a millimeter, it may cause serious image defects. So, if you can afford it, try to buy high-end lenses, or at least assemble them more carefully.
The influence of optical axis deviation on the image is that the imaging of local area is not clear. For example, the definition of one of the four corners of a photo is obviously poor, which is basically caused by the deviation of the optical axis. Or, half of the images are unclear, which is also an optical axis deviation (or the camera cmos itself is biased).
If a photo is not clear near the edge, strictly speaking, the range of a circle radiated from the center of the photo is not clear. This is not a fault, but the phase field is bent or the edge resolution is weakened, which belongs to the choice in lens design. Wide-angle lenses generally have the phenomenon of phase field bending and edge resolution weakening, and even some top lenses can't escape this list.
The damping oil of the optical axis 3 of the fixed-focus lens is grease coated on the relevant parts of the lens focusing mechanism or zoom mechanism. Its function is to produce a corresponding damping feeling, which brings a better user experience when zooming or focusing.
Because the relevant parts of the lens zoom mechanism and focus mechanism are coated with damping oil, if the damping oil is to be replaced, the lens must be disassembled. This may affect the structure of the lens group and produce optical axis deviation. Once this happens, the optical axis must be calibrated.
If the replacement of damping oil is done by professionals, there will be no problem. Even if it really causes the optical axis deviation of the lens, it can be easily calibrated back ... After all, people are professionals ... But if the operation of replacing damping oil is operated by amateurs, problems may arise ... Because of unskilled technology, the original structure of the lens may not be restored, and if the optical axis is to be calibrated, the lens cannot be used normally ... So for non-professionals, don't try to disassemble and repair the lens yourself.