In machine vision systems, ordinary lenses have many uses. In fact, many machine vision projects can be done with these lenses. But in some projects, the image provided by these lenses is not suitable; In this case, depending on the need, we can use more complex lenses such as telecentric lenses, 360 lenses and macro lenses. In this article, the different types of these lenses are described.

1- Normal lenses

These types of lenses are used in most machine vision projects. Normal lenses are very widely used and have a function similar to the human eye. In other words, they see closer objects as bigger.

Features of normal lenses

• They have different types (in terms of lens opening, working distance, resolution, etc ) .
• Normal lenses are widely used and are used in many machine vision projects.
• They generally have a fixed focal length.
• The price of normal lenses is relatively cheap.

2- telecentric lenses

Telecentric lenses are generally used for precise measurements in machine vision. Telecentric lenses have many advantages over conventional lenses. An example of these lenses is shown in the figure below.

Characteristics of telecentric lenses

• The image taken from these lenses does not change by changing the working distance (the distance between the object and the lens).
• These lenses provide precise edges and are suitable for measurement.
• The image of telecentric lenses is without distortion.
• These lenses are relatively expensive and their weight is high.

The images of several different objects taken using a telecentric lens and back lighting are shown below. is displayed.

3- 360 degree lenses

Suppose we want to see the outer environment of an object, for example a screw, using ordinary lenses; In this case, we need to use 3 or 4 lenses and cameras so that each camera can see some of the outside environment. For example, in the picture, three cameras are used to detect whether the bottle cap is closed.

360 degree lenses allow us to see the inside or outside of an object using only one lens. These lenses provide us with a place to reduce the number of components in a machine vision system. There are different types of 360 lenses, each of which is designed for a specific purpose. In the following, we will examine some examples of these lenses.

Seeing the external views of an object

We can use special lenses to see the external aspects of an object. These lenses take multiple pictures of different faces of the object by using the mirrors inside them. The picture below shows an example of these lenses made by Opto.

The image taken of a bead and ampoule glass by this lens is shown in the figure below. In these images, 8 different faces of the object can be seen, and with the help of it, it is possible to check various errors on the external views of an object.

Hole Identification

Suppose we want to check the threads inside a nut. In this case, the threads will not be visible with the image taken by the normal lens. Therefore, we must use special lenses to identify the inside of a cavity or hole. The picture below shows some examples of these lenses.

Suppose we put a bead under one of these lenses as shown in the figure below.

In this case, the image of this bead will be as shown below, where the threads will be visible.

Using the polar filter in Halken software we can Convert the above to the following image and finally find the error by programming on the images:

Print Check

To check the print in 360 degrees, we can use the lens shown in the picture.

Suppose we place an object whose outer environment has a print under this lens. In this case, the output image of this lens will be as shown in the picture.

By using the polar filter in Halken software, we can convert the above image into the below image and finally find the error by programming on the images.

4- Macro lenses

Shooting small objects with normal lenses causes image distortion and reduces image resolution. To solve this problem, we can use macro lenses. These lenses are designed in such a way that they have very little image distortion and provide high resolution images. With the help of macro lenses, we can take high-quality images of small objects. A macro lens is shown in the picture below.

Features of macro lenses

• These lenses can be used to photograph small objects.
• Image distortion is very low in these lenses.
• They provide good clarity and image quality.
• They are suitable for measuring dimensions.
• They usually have a small working distance.

The image below shows a small flake imaged using a macro lens.

The picture below shows that if we take a picture of a screw with a macro lens (using front lighting), we can check its threads.

Summary and results

In this article, the types of lenses used in machine vision are explained and the following results were obtained:

1. In many machine vision projects, we can use ordinary lenses.
2. If we need accurate measurement, we can use tele lensesLet’s use centric.
3. To see the external or internal environment of an object, depending on the need, we can use 360 lenses.
4. If we want to see a small object with high resolution and without disturbance, we use macro lenses.

In machine vision training course with Halcon software, we teach you how to use machine vision for different types of projects. Choose the right lens. You can also get consultation to choose a lens.

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