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Distortion, also known as distortion, is due to the influence of spherical aberration of the diaphragm. The chief ray of the divided field passes through the optical system and differs from the Gaussian image. The intersection height of the plane is not equal to the height of the ideal image. The difference between the two is distortion. Simply put, it is the degree of distortion of the image formed by the optical system on the subject relative to the object itself. Therefore, distortion only changes the imaging position of the off-axis object point on the ideal surface, causing distortion in the shape of the image, but does not affect the clarity of the image.
Distortion can be divided into positive and negative. Divided into pincushion distortion and barrel distortion.
Distortion types
Distortion usually has two calculation methods: optical distortion (Op tical distortion ) and TV distortion, the calculation method is:
How to use the parameters of lens distortion to calculate the measurement error?
If the camera chip is 2. /3′ (diagonal is 11mm, pixel size is 3.45um), the optical distortion rate of a certain lens is dist=0.05 %, with y=5.5mm, then Δy=dist*y/100=0.05%x5.5mm/100=2.Rwanda Sugar Daddy75µm. Therefore, the distortion causes the image to shift by 2.75µm, which is less than one pixel.
It is recommended to check the situation. The distortion rate of Molite MML series telecentric lenses and ML-MCHR series macro lenses is extremely small ( 0.0x%~0.00x%), usually no distortion correction is required, so it is very convenient to use
Telecentric lens and telecentricity
When viewed by the human eyeRwanda Sugar When looking at the same object, when it is close, the object feels larger, and when it is far away, the object feels farther away. This phenomenon is called perspective error. Generally This phenomenon also occurs with lenses, but when used for measurement, perspective errors will bring measurement errors, so a telecentric lens is usually needed to eliminate perspective errors.
The commonly used telecentric lenses in the field of mechanical vision are: object far away Rwandans Escort telecentric lens and bilateral Telecentric lens.
An object-side telecentric lens sets an aperture diaphragm at the image-side focal point of the lens so that the principal ray at the off-axis point is parallel to the optical axis.
Bilateral telecentric lens. This is accomplished by setting the aperture diaphragm at both the object side and the image side focal plane.
For most applications, since the flange distance from the camera chip to the lens interface is fixed, there is only perspective error caused by changes in the distance of the object within the object depth of field. At this time, the object telecentric lens can suffice. Requested only when the distance from the chip to the flange of the lens interface is variable due to the device or camera chipRwandans Escort precision. , it is necessary to use bilateral telecentric lenses to eliminate perspective errors caused by the object side and the imageRwanda Sugar rwanda-sugar.com/”>RW EscortsPoor. MML series are object-direction telecentric lenses, and MTL series are bilateral telecentric lenses.
Experienced engineers will find that the differences Telecentric lenses also vary in their ability to eliminate perspective errors. This is because the telecentricity is defined as the angle θ between the main ray and the optical axis.
Assume that the height difference of the object is d=2mm. Telecentricity θ=0.05°, then the object position offset =2mm*tan0.05°=1.7µm. If an ordinary lens is used, θ=15°, the object position offset =2mm*tan15°=535.9µm. For the measurement of non-stereoRW Escorts objects, only a telecentric lens with high telecentricity can effectively eliminate the perspective error, thus Reduce measurement errors. Most of the telecentricity of Molite telecentric lenses is 0.0x°.
In addition, most engineers have misunderstandings about depth of field and telecentricity, thinking that the depth of field of telecentric lenses is greater than that of ordinary lenses. Big. But we have discussed depth of field specifically in previous issues, and we understand that depth of field is only related to the diameter of the diffuse spot, lens Fno., magnification, and telecentricity.
The advantages of telecentric lenses: (1) The most important. The outstanding feature is the elimination of perspective errors; (2) Generally, telecentric mirrors RW EscortsThe distortion of the head is very small; (3) The absolute illumination of all telecentric lenses is very good.
Telecentric lens failure: Due to the limitation of the telecentric optical path, the barrel diameter of the telecentric lens is > FOV. Therefore, when the object to be measured is large, the telecentric lens will be very bulky and costly.
The machine vision product material query platform provides more information about industrial lenses.
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