The main parameters of the lens
1. Focal Length
Focal length is the distance between the center point of the lens and the clear image formed on the glue plane. The size of the focal length determines the size of the viewing angle, the small value of the focal length, the large angle of view, and the large range of observation; The focal length value is large, the angle of view is small, and the viewing range is small. According to whether the focal length can be adjusted, it can be divided into two categories: fixed focus lens and zoom lens.
2. Aperture (Iris)
It is denoted by F and measured as the ratio of the focal length f of the lens to the clear aperture D. Each lens is marked with a maximum F-number, such as 8mm / F1.4 for a maximum aperture of 5.7mm . The smaller the F-number, the larger the aperture, and the larger the F-number, the smaller the aperture.
3. Compatible with the maximum CCD size (Sensor Size)
The maximum CCD chip size that can be covered by the lens imaging diameter. Mainly: 1/2", 2/3", 1" and 1" or more.
4. Mount
How the lens is connected to the camera. Commonly used ones include C, CS, F, V, T2, Leica, M42x1, M75x0.75, etc.
5. Depth of Field (DOF)
Depth of field refers to the extent to which the image of the subject remains clear within a certain distance before and after the subject is in focus. The depth of field varies depending on the aperture value, focal length, and shooting distance of the lens. The larger the aperture, the smaller the depth of field; The smaller the aperture, the greater the depth of field. The longer the focal length, the smaller the depth of field; The shorter the focal length, the greater the depth of field. The closer you get to the subject, the smaller the depth of field; The farther away from the subject, the greater the depth of field.
6. Resolution
Resolution represents the ability of a lens to record the details of an object, measured in terms of the number of black and white lines that can be resolved per millimeter: "line pairs" per millimeter (lp/mm). The higher the resolution, the clearer the image.
7. Working distance (WD)
The distance from the first working surface of the lens to the object to be measured.
8. Field of View (FOV)
The size of the area actually captured by the camera.
9. Optical magnification (Magnification,)
CCD/FOV, which is the chip size divided by the field of view.
10. NumericalAperture (NA)
The numerical aperture is equal to the product of the sinusoidal value of the refractive index n of the medium between the object and the objective lens and half of the aperture angle of the objective lens (a2), and is calculated by the formula N.A=n*sin a/2. The numerical aperture is closely related to other optical parameters, it is directly proportional to the resolution and proportional to the magnification. That is to say, the numerical aperture directly determines the resolution of the lens, the larger the numerical aperture, the higher the resolution, otherwise the vice versa.
11. Flange distance
To be precise, the back zoom is a parameter of the camera, which refers to the distance from the camera interface plane to the sensor. However, when selecting a lens for an in-line scan lens or a large area scan camera, the back zoom is a very important parameter because it directly affects the configuration of the lens. Cameras from different manufacturers may have different back zooms even if they have the same interface.
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