Main Parameters Of 3D Vision Sensor Lens
The optical system of 3D Vision Sensor Lens is generally composed of several groups of lenses. Each group of lenses may be a single lens, or it may be composed of two or more single lenses glued together.
Machine vision lenses are thick lenses. However, in most cases, the geometric relationship and parameter calculation of thin lens can be used as the basis for lens selection.
Main parameters of 3D Vision Sensor Lens
Field of view: or field angle, the range that the image acquisition device can cover, that is, the size of the object plane corresponding to the image on the target surface;
Working Distance: generally refers to the distance from the front end of the lens to the object to be measured. Systems that are less than the minimum working distance generally cannot image clearly;
Depth of Field: Centered on the WD when the lens is optimally focused, there is a range in front of and behind the lens, within which the lens can image clearly.
Relative aperture: refers to the ratio of the diameter of the incident optical aperture (D) to the focal length (f) of the lens, namely D/f;
Maximum relative aperture: it is usually marked on the lens, such as 1:1.2 or f/1.2;
Aperture coefficient: The reciprocal of the relative aperture is called the aperture coefficient, which is expressed in F.
Resolution
It refers to the number of black and white stripes that can be resolved by the lens in unit mm at the image plane. The resolution is 1/2d, and d is the line width. The unit is “pair/mm” (lp/mm)
Resolution The distance between the resolved stripes on the focal plane of an ideal lens is
δ= one point two two λ·F The reciprocal is the resolution of the ideal lens, λ Is the wavelength of light, and F is the aperture coefficient value NL=1/(1.22 λ· F)
Most cheap lenses have a resolution of 50lp/mm, which is equivalent to a horizontal resolution of 700 pixels. They are used for vision systems with low resolution requirements, and are matched with cameras with a resolution below VGA.
The lens with a resolution of 100lp/mm and above can be used for the lens with a megapixel level or above, which is matched with a camera with a horizontal resolution of 1280.
Main factors affecting resolution:
Lens structure, material, processing accuracy, etc.
Other factors:
The larger the aperture of the lens, the higher the resolution;
The shorter the wavelength, the higher the resolution;
Fixed focus lenses of the same grade have higher resolution than zoom lenses;
The edge resolution of the short focus lens is generally lower than that of the center, and the center resolution of the long focus lens is generally lower than that of the edge.
The depth of field is related to the focal length, aperture and object distance of the lens:
The smaller the aperture, the greater the depth of field
The greater the shooting distance, the greater the depth of field;
The shorter the focal length, the greater the depth of field.
3D Vision Sensor Lens distortion
The straight line outside the main axis in the subject plane becomes a curve after being imaged by the optical system, and the imaging error of this optical system is called distortion.
Distorted aberration only affects the geometric shape of imaging, but does not affect the clarity of imaging.
Distortion is defined as the difference y ‘- yo’ between the actual image height y ‘and the ideal image height yo’. In practical applications, the percentage of its ratio to the ideal image height yo ‘is often used to represent distortion, which is called relative distortion
The short focus lens generally shows barrel distortion, while the long focus lens generally shows pillow distortion.
The human eye cannot sense the distortion less than 2%. Distortion needs to be corrected when measuring with high accuracy!
Fixed Lens
Zoom lens
Special lens
Macro
Microlens
Telecentric
Infrared
Ultraviolet lens
Classification of shots
Fixed focus lenses are divided into:
Fish eye lens: 6-16mm
Ultra wide angle lens: 17-21mm
Wide angle lens: 24-35mm
Standard lens: 45-75mm
Long focus lens: 150-300mm
Ultra long focal lens: above 300mm
Machine vision lenses are thick lenses. However, in most cases, the geometric relationship and parameter calculation of thin lens can be used as the basis for lens selection.
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