When evaluating the quality of industrial lens, several practical parameters such as resolution, sharpness and depth of field are very important.
It is also known as discrimination rate and resolution, which refers to the ability of the lens to clearly distinguish the fiber details of the subject. The factor that restricts the resolution of industrial lens is the phenomenon of diffraction of light, that is, the diffraction spot (airy disk). The unit of resolution is "line pair/mm" (lp/mm).
It is also called contrast, which refers to the contrast between the bright and dark parts of the image.
In the scenery space, the scenery located within a certain distance before and after the plane of focusing object can also be captured with a relatively clear image. The above-mentioned depth distance between the scenery that enables to form a relatively clear image before and after the focusing object plane is the depth range of the scenery space that can obtain a relatively clear image on the actual image plane, which is called the depth of field.
The relative aperture refers to the ratio of the diameter of incident light aperture (indicated by D) to the focal length (indicated by f) of the industrial lens, namely: relative aperture=D/f.
The reciprocal of the relative aperture is called aperture scale, also known as f/system aperture scale or aperture number. The relative aperture of a general lens can be adjusted, and its relative aperture or aperture scale is often marked on an industrial lens, such as 1:1.2 or f/1.2.
If the light at the shooting site is low or the exposure time is short, you need to choose an industrial lens with a relatively large aperture as much as possible.