The solution to the blurry surface defect image

Telecentric lenses are a category of optical lenses characterized by their ability to maintain a constant image size regardless of the object’s position relative to the lens. This is achieved by ensuring that the chief rays—those rays that pass through the center of the lens—are parallel to the optical axis, and therefore, the object distance does not affect the image size. The concept of telecentricity is central to the design of lenses used in high-precision applications, such as optical metrology, 3D scanning, and surface defect inspection. Unlike conventional lenses, which suffer from perspective distortion as the object moves closer or farther from the lens, telecentric lenses ensure that the image remains undistorted and of constant size, a critical feature in many industrial and scientific applications.

The working principle behind a telecentric lens can be described as follows: light rays coming from an object pass through the lens in such a way that they all travel parallel to each other along the optical axis. The result is an image that does not suffer from the common optical distortions such as barrel or pincushion distortion. Additionally, the magnification factor is independent of the object’s distance from the lens, which makes telecentric lenses ideal for imaging systems where precise measurement and dimensional accuracy are paramount.

These properties are particularly advantageous in high-precision measurement systems, where even slight distortions or changes in the object’s distance could result in inaccurate readings. Moreover, telecentric lenses are highly sought after in environments where objects must be measured from multiple angles or at various distances without affecting the overall image quality.

In industrial applications, surface inspection plays a critical role in maintaining product quality and ensuring that components meet the required specifications. Surface defects, including scratches, dents, cracks, or discoloration, can often go unnoticed with conventional imaging techniques, especially when the object being inspected has intricate details or is subject to variations in surface reflectivity. A major challenge in these scenarios is achieving consistent and even illumination across the object’s surface, particularly when the inspection area is small or when the object is irregularly shaped.

Coaxial illumination is often employed to address these issues. Coaxial light sources are positioned along the same optical axis as the camera or imaging system, meaning the light comes directly from the lens’ perspective. This type of lighting helps to minimize shadows and reflections, offering an even distribution of light across the surface of the object. However, coaxial illumination systems can face challenges related to working distance and the design of the light source itself. If the working distance is too short or the design of the illuminator interferes with the lens or the imaging setup, the resulting images may be unclear or improperly lit, making defect detection difficult.

Despite these challenges, coaxial illumination remains one of the most effective methods for surface inspection. However, achieving the optimal conditions for both illumination and imaging requires careful consideration of the optical system’s design, including the choice of lens, lighting configuration, and working distance.

Telecentric lenses offer a significant advantage when used in conjunction with coaxial illumination systems. One of the primary reasons why telecentric lenses are so valuable in surface inspection applications is their ability to eliminate perspective distortion. This ensures that the surface details are captured without the image size changing as the object moves or as the camera adjusts its position. As mentioned earlier, telecentric lenses help to maintain a constant image size and minimize any optical distortions, providing the clarity and precision needed for surface defect detection.

The key advantage here is that telecentric lenses allow for consistent measurements to be taken from the object’s surface, even when the object is positioned at different distances from the camera or when it is moving along a production line. This ensures that even small variations or defects on the object’s surface can be accurately captured and analyzed.

Given the demands of modern surface inspection systems, the need for a telecentric lens that offers both high precision and the ability to function in constrained spaces is critical. The Basson SUT065 series 2x telecentric lens is an excellent example of a lens designed to meet these needs.

This particular lens is designed with a short working distance in mind, which is essential when dealing with applications where the inspection space is narrow or where the object is small. Despite its compact size—less than 100mm in length—the Basson SUT065 series 2x telecentric lens maintains telecentricity and a distortion rate of less than 0.05%. This ensures that the image produced by the lens is of the highest quality, with minimal optical distortion, even when the object is positioned at varying distances.

A significant advantage of this lens is its coaxial design, which integrates the illumination system with the lens itself. This design ensures that light is directed uniformly across the object’s surface, providing consistent and even lighting. Achieving uniform illumination is particularly important in surface defect inspection, as it reduces the likelihood of shadows or uneven light distribution that could obscure defects or distort the image. With a uniformity rate of over 90%, the Basson SUT065 series 2x telecentric lens ensures that surface defects are captured clearly and without the interference of lighting inconsistencies.

The coaxial design also addresses one of the common challenges in optical inspection systems: interference between the lens and the illuminator. In many cases, the lens of the coaxial illuminator can obstruct the optical path, leading to suboptimal image quality. However, the design of the SUT065 series lens minimizes this risk by optimizing the placement and size of the lens elements, ensuring that both the imaging system and the illumination system work together harmoniously.

Uniform illumination is one of the most critical aspects of any surface inspection system, as it directly affects the ability to detect surface defects. Even minor imperfections can be difficult to spot without consistent and uniform lighting, especially in cases where the surface material may have varying reflectivity or texture. Non-uniform lighting can create shadows or bright spots, which can obscure important features or defects on the object’s surface.

In some cases, it can lead to false positives or negatives, where the system incorrectly detects defects due to variations in light intensity or angle. The Basson SUT065 series 2x telecentric lens helps to mitigate these issues by providing uniform illumination, ensuring that the surface is lit evenly and that defects are captured with clarity. This consistency is essential in industrial inspection systems, where reliability and accuracy are key factors in maintaining product quality and preventing defects from reaching consumers.

Moreover, uniform illumination aids in ensuring repeatability in inspection processes, allowing the system to reliably detect the same defects over time and across different production batches. This level of consistency is vital for industries such as electronics manufacturing, automotive production, and quality control in precision engineering, where high standards of quality assurance are required.

The versatility of the Basson SUT065 series 2x telecentric lens makes it suitable for a wide range of applications beyond surface defect detection. In addition to surface inspection, this lens is also ideal for precise measurement tasks, including dimensional measurement, alignment, and 3D imaging. The high precision and low distortion rate make it an invaluable tool in industries such as electronics, pharmaceuticals, and medical device manufacturing, where accuracy and reliability are critical.

The lens is also suitable for use in automated inspection systems, where objects are moving along a production line. In such applications, maintaining a consistent image quality is essential for ensuring that defects or variations are detected quickly and accurately. The ability to achieve precise measurements and clear imaging in such systems makes the SUT065 series 2x telecentric lens a valuable asset for any industrial inspection process.

Basson focuses on machine vision products used for precision measurement and defect detection.

Basson not only provides high-precision bi-telecentric lens systems, telecentric lens systems, telecentric light sources, coaxial illuminations and optical lenses, but also offers customized services.

With products designed in Germany, business planned in the UK and products made in China, Basson is able to provide superior products to customers through its global team. Currently, Basson is in preparation of production and assembly of products in Japan.

Dr. Liu Lu, acting as CTO of Basson, is a PhD degree holder of Oxford University.

Production and testing instruments include optical vacuum coating machines manufactured by Satis in Switzerland and Leybold in Germany, a laser interferometer from Zygo in the US, a spectrophotometer from PerkinElmer in the US, a spherometer from Hofbauer Optik in Germany, a centering instrument from Kyoritsu Electric in Japan, a NC grinding device made by Kojima Engineering in Japan and an automatic centering machine made by Shonan in Japan.