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A large number of machine vision projects with Normal lenses can be done. But in some projects, we cannot get a good answer with normal lenses. In these cases, we need to use more advanced lenses such as telecentric lenses and macro lenses. Due to their special features, telecentric lenses can be used in cases such as measurement. In this article, we examine the four advantages of telecentric lenses that make these lenses superior to normal lenses. The image of a telecentric lens is shown in the figure below.
1- Fixed image for changing distance, the important feature of telecentric lens
One of the important features of telecentric lenses is the fixed image per distance change. In telecentric lenses, if the distance of the object from the lens increases or decreases, the image received from the camera is fixed. To understand this concept, pay attention to the image below. In this picture, two screws with the same size have been photographed. The distance of one of the screws is greater than the lens.
The image on the right is taken from a normal lens, where the screw that is farther from the lens appears smaller. The image on the left was taken using a telecentric lens where the size of the screws in the image is constant.
2- Image without distortion advantage of telecentric lens
In telecentric lenses, the image is not distorted. To understand this concept, a calibrated plate has been photographed under different conditions as shown in the figure below. The image on the right shows the trapezoidal distortion, the middle image shows the radial distortion, and the image on the left shows the image received from the telecentric lens, which we will explain below.
- Trapezoidal distortion (picture on the right)
This disturbance is caused by the tilt of the calibration plate. This disturbance causes the square shapes on the calibration screen to appear trapezoidal in the image. For this reason, this type of disturbance is called a trapezium.
- Radial distortion (middle image)
- image without distortion from telecentric lens (left image)
The image received from the telecentric lens is without distortion and there is no trace of radial and trapezoidal distortion.
3- resistant to changing the position of the object on the page
Another important feature of telecentric lenses is that if we change the object in the plane where it is located, the received image does not change. To understand this concept, see the image, in which a number of cylindrical objects are placed under the camera.
In the figure on the left, the received image of these objects with a normal lens is displayed. As you can see in this image, the appearance of cylindrical objects changes depending on its position. In other words, the image received from each of them is different from the normal lens. While in telecentric lenses, the image received from them (picture on the right) is the same.
4- Precise edges in images, superiority of telecentric lens
Image edges are more accurate in telecentric lenses. To understand this concept, pay attention to the image below. where the bright dark border of the image is magnified. As you can see in the picture, the border of darkness and brightness in normal lenses is much higher than telecentric lenses. This makes telecentric lenses more suitable for certain applications such as measurement.
Summary
In this article, we provided explanations about telecentric lenses. In some applications, such as dimensional measurement, these lenses provide a favorable image. The price of these lenses is higher than normal lenses, that’s why we go to them when we can’t get answers from normal lenses. If you need more information about this, you can use our consulting services.
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