Industrial lenses are important imaging components in machine vision systems. If the system wants to fully perform its functions, industrial lenses must be able to meet the requirements. At the beginning of the 21st century, with the wide application of machine vision systems in the field of precision inspection, it is difficult for ordinary industrial lenses to meet the testing requirements. In order to make up for the shortcomings of ordinary lens applications and adapt to the needs of precision detection, telecentric lenses have emerged.

Telecentric lenses are based on their unique optical properties: high resolution, ultra-wide depth of field, ultra-low distortion and unique parallel light design, which brings a qualitative leap to machine vision precision inspection. Telecentric lenses are based on their unique optical properties: high resolution, ultra-wide depth of field, ultra-low distortion and unique parallel light design, which brings a qualitative leap to machine vision precision inspection.

What is a far lens?

Telecentric is mainly designed to correct the parallax of traditional industrial lenses. It can make the image magnification not change within a certain object distance range. This is the case that the measured object is not on the same object surface. It is a very important application. Telecentric lenses have always been favored for machine vision applications where lens distortion is critical due to their unique parallel light path design.

　　 Far lens principle advantage

The purpose of the telecentric lens is to eliminate the inconsistency in the distance between the measured object (or CCD chip) from the lens, resulting in different magnification. According to the telecentric lens classification design principles are:

1) The design principle and function of the object side telecentric light path:

The object-distance optical path is to place the aperture stop on the image focal plane of the optical system. The main ray of the object is parallel to the convergence center of the main ray of the optical axis. The object is infinity, called the object-side telecentric light path. Its function is: it can eliminate the reading error caused by inaccurate focusing.

2) The principle and function of the design of Fang Yuanxinguang Road:

Like Fang Yuanxinguanglu, the aperture stop is placed on the object focal plane of the optical system. The convergence center of the principal ray parallel to the optical axis is located at infinity on the object side. It is called: Fangyuanyuanguanglu. Its function is: it can eliminate the measurement error that the image focus is not allowed to introduce.

3) Design principles and functions of the telecentric optical paths on both sides:

It combines the dual role of the object side/image side telecentricity. Mainly used in the field of visual measurement and detection.

Application advantage

Telecentric lenses are mainly used for precision measurement. In the precision optical measurement system, the ordinary optical lens has certain constraints, such as image deformation, error caused by viewing angle selection, and boundary uncertainty caused by inappropriate light source interference, which affects the accuracy of measurement. Telecentric lenses can effectively reduce or even eliminate the above problems, so Telecentric lenses have become the decisive component of precision optical measurement systems, and their application fields are becoming more and more extensive.

　　 How to choose the far lens

In these years, machine vision has developed rapidly in China. Everyone has a certain understanding of the selection of ordinary lenses in system integration, but the selection of telecentric lenses is often confused, even with the help of technicians. Lens, I still don't know what to pay attention to during the use. In response to this problem, the principle of matching the telecentric lens and the camera is the same as that of a normal industrial lens, as long as the size of the target surface is greater than or equal to the target surface of the camera. Please pay attention during use. Telecentric imaging is performed in the area below the objective lens of the telecentric lens. The area beyond this range is not strictly telecentric imaging. This must be used in actual use. Note that otherwise unnecessary deviations will occur.

When choosing a telecentric lens, the customer should first understand when to choose the telecentric lens when needed. According to the principle characteristics and unique advantages of the telecentric lens, when the inspection object encounters the following 6 conditions, it is best to use the telecentric lens:

1) When it is necessary to detect objects with thickness (thickness > 1/10 FOV diameter); 2) When it is necessary to detect objects that are not in the same plane; 3) When it is not clear what the distance from the object to the lens is; 4) When needed When detecting an object with aperture and three-dimensional shape; 5) When low distortion is required and the brightness of the image effect is almost identical; 6) When the defect is detected only in parallel illumination in the same direction.

Depending on the usage (object size and resolution required), select the object size lens and CCD or CMOS camera with the appropriate object size, and obtain the image size to calculate the magnification. Then select the appropriate image lens according to the product list. . During the selection process, attention should also be paid to the influence of the depth of field indicator, because the larger the image/object magnification, the smaller the depth of field, and in order to obtain a suitable depth of field, it may be necessary to reselect the lens.

Contrast with normal lens

The telecentric industrial lens is mainly designed to correct the parallax of traditional industrial lenses. It can be used within a certain object distance range, so that the image magnification will not change with the object distance. The situation that is not on the same surface is a very important application.

The closer the general industrial lens target object is to the lens (the shorter the working distance), the larger the image will be. When using a normal lens for dimensional measurement, there are the following problems:

1) Since the objects to be measured are not in the same measurement plane, the magnification is different; 2) the lens distortion is large; 3) the parallax is also when the object distance becomes larger, the magnification of the object also changes; 4) the lens analysis Not high; 5) Uncertainty of the edge position of the image due to the geometrical characteristics of the visual source.

The telecentric lens can effectively solve the above problems of the ordinary lens, and there is no judgment error of this nature, so it can be used in high-precision measurement, measurement and measurement. The telecentric lens is a high-end industrial lens that usually has superior image quality and is especially suitable for dimensional measurement applications.

No matter where, at a certain working distance, there will be the same magnification after refocusing, because the maximum field of view of the telecentric lens is directly related to the proximity of the lens. The larger the lens size, the more the scene is needed. Big. The telecentric measuring lens provides superior image quality, and the distortion is smaller than that of the conventional fixed-focus lens. This optical design makes the image surface more symmetrical and can be precisely measured with software.

Common lens advantages: low cost, practical, and versatile.

Common lens disadvantages: Magnification will change, there will be parallax.

Ordinary lens application: imaging of large objects.

Advantages of the telecentric lens: the magnification is constant, does not change with the depth of field change, and has no parallax.

Disadvantages of telecentric lenses: high cost, large size, and heavy weight.

Telecentric lens application: measurement and measurement, based on CCD measurement, microcrystallography