The Principle, Selection, Main Features And Applications of Telecentric Lenses

A telecentric lens is an industrial lens with a special optical design that can keep the image magnification constant within a certain object distance range, thereby eliminating perspective errors and maintaining absolute accuracy in object size measurement. It has important applications in machine vision, industrial inspection, and precision imaging.

1.The principle of telecentric lens

The basic principle of a telecentric lens is to use a special optical design to keep the light in the imaging system parallel in the object space and image space. This ensures that the size of the image remains constant when the object moves within the depth of field, that is, the image will not appear larger when it is closer and smaller when it is farther away. This characteristic is mainly achieved through a special lens combination:

Object-space telecentric lens: The aperture stop is placed on the image-side focal plane, and the light is regarded as coming from infinity, thus eliminating perspective distortion.

Image-space telecentric lens: The aperture diaphragm is placed on the object-space focal plane to ensure uniform illumination on the image plane.

Bi-telecentric lens: Combining object-space and image-space telecentric designs to further eliminate or reduce measurement errors.

The principle of telecentric lens

2.Selection of telecentric lenses

The selection of telecentric lenses needs to be comprehensively considered according to the specific application scenario requirements. The following are several main considerations:

Field of view size

The field of view (FOV) determines the range of objects a lens can capture. A larger FOV is suitable for wide-area inspections, while a smaller FOV is suitable for high-precision, localized inspections. The object being measured and the size of the field of view can be referred to the formula: magnification β = sensor size / field of view size.

Working distance

The working distance of a telecentric lens refers to the distance between the front of the lens and the object being measured. Different applications may require different working distances. For example, industrial inspection may require a longer working distance, while microscopic measurement may require a shorter working distance.

Focal length

The focal length determines the magnification and imaging range of the lens. Short focal lengths are suitable for wide-angle imaging, while long focal lengths are suitable for long-distance imaging.

Resolution and depth of field

Resolution determines the clarity of the image, while depth of field affects the depth range of imaging. Lenses with high resolution and large depth of field are suitable for applications that require high precision and large-range detection.

Aperture size

The aperture size affects the amount of light entering the lens. A larger aperture can achieve better imaging effects in low light conditions.

Selection of telecentric lenses

3.Main features of telecentric lenses

The special optical design gives the telecentric lens the following significant features:

Zero perspective and no parallax. Because the light rays are parallel, the imaging system does not experience parallax due to changes in the object’s position. For example, height differences or positional offsets do not affect the measurement results. This is very important for measuring non-planar objects.

High resolution. Telecentric lenses typically have high resolution, capable of capturing detailed images. They are suitable for precision measurement and high-resolution imaging, such as detecting microstructures such as chip line width and screen pixel defects.

Low distortion. The design of telecentric lenses can usually effectively reduce distortion problems, improve imaging quality and measurement accuracy.

Large depth of field. Telecentric lenses have a large depth of field, which can maintain clear imaging at a deeper range and reduce image blur caused by insufficient depth of field.

Strong environmental adaptability. Telecentric lenses have high optical path stability and low sensitivity to vibration and temperature changes. They can adapt to complex environments such as factory workshops and are suitable for various industrial scenarios such as semiconductor testing, electronic component measurement, and gear testing.

Main features of telecentric lenses

4.Core applications of telecentric lenses

Telecentric lenses are widely used in many fields, including but not limited to:

Machine vision

In machine vision systems, telecentric lenses are primarily used for high-precision part inspection, dimensional measurement, and surface defect detection. For example, in a laser welded butt joint gap width vision measurement system, a telecentric lens is used to accurately detect the weld boundary and joint gap width.

Industrial inspection

Telecentric lenses are primarily used in industrial inspection to detect product size, shape, and surface defects. For example, in wear particle image online inspection technology, telecentric lenses are used to improve inspection efficiency and accuracy.

Microscopic measurement

Telecentric lenses are used in microscopic measurement for high-precision microstructure analysis and measurement. For example, in microscopic 3D measurement technology, telecentric lenses are used to improve measurement accuracy.

Semiconductor manufacturing

Telecentric lenses are also commonly used in semiconductor and electronics manufacturing, mainly for wafer defect detection, chip packaging measurement, etc.

Core applications of telecentric lenses

Medical testing

In medical applications, telecentric lenses are mainly used for high-precision microscope imaging and pathological section analysis, such as performing cell nuclear morphology analysis to avoid misdiagnosis caused by blurred edges.

Scientific research

In scientific research, telecentric lenses are mainly used for high-resolution imaging and precise measurement, such as nanoindentation deformation observation, with a dynamic tracking accuracy of 10nm.

In addition, telecentric lenses are also used in space infrared detection for large-range imaging, high-sensitivity detection, and high-precision positioning.

In short, telecentric lenses play an important role in industrial automation and precision measurement due to their unique optical properties and superior performance. Choosing the right telecentric lens requires comprehensive consideration of the application scenario, selecting appropriate parameters and design to achieve optimal measurement results and image quality.