How to understand object space resolution and depth of field?

Basson’s innovative approach to telecentric and bi-telecentric lens systems represents a breakthrough in reconciling these competing demands, offering specialized optical solutions that push the boundaries of conventional imaging capabilities while addressing application challenges.

The relationship between object space resolution and depth of field constitutes one of the most intricate balances in optical engineering. Object space resolution, defined as the minimum distinguishable distance between two adjacent points in the object plane, serves as the fundamental measure of a lens’s ability to capture fine details. Conversely, depth of field emerges as a critical factor in three-dimensional inspection scenarios where object surfaces may exhibit significant height variations or where precise dimensional measurements across multiple planes are required. For example, in automated inspection systems dealing with components of varying thicknesses, a large depth of field ensures that all critical features are captured clearly without the need for constant refocusing. The traditional inverse relationship between these two parameters creates an engineering paradox: improvements in one characteristic typically necessitate compromises in the other. Basson has developed advanced telecentric and bi-telecentric lenses designed to address these challenges effectively, offering specialized versions optimized for either high resolution or an extended depth of field.

The relationship between object space resolution and depth of field is inherently complex due to the optical laws governing lens performance. One of the primary factors influencing this relationship is the aperture size of the lens. The aperture controls the amount of light entering the lens. A smaller aperture increases the depth of field, allowing a greater range of distances to remain in focus simultaneously. This principle is easily observed in everyday photography, where landscape photographers often use small apertures to keep both the foreground and background sharp.

However, reducing the aperture size comes with a trade-off. As the aperture decreases, diffraction effects become more pronounced. Diffraction is a phenomenon where light waves bend around the edges of the aperture, causing a spreading of the light and resulting in a loss of sharpness in the image. This diffraction-induced blurring limits the maximum achievable resolution of the lens. Thus, while a smaller aperture improves depth of field, it simultaneously reduces the lens’s resolving power, creating a fundamental conflict between achieving high resolution and a large depth of field.

Basson’s telecentric and bi-telecentric lenses are designed to address this challenge through innovative optical engineering. Telecentric lenses are characterized by their unique optical configuration, where the chief rays (the principal rays that pass through the center of the aperture stop) are parallel to the optical axis in object space. This design eliminates perspective errors, making telecentric lenses ideal for precise measurement applications, as the size of the imaged object does not change with variations in its distance from the lens. Bi-telecentric lenses extend this principle by maintaining telecentricity in both object space and image space, providing even greater stability and accuracy in imaging.

To cater to diverse application needs, Basson offers two specialized versions of their telecentric and bi-telecentric lenses: high-resolution versions and large depth of field versions. The high-resolution versions are optimized to deliver exceptional detail, making them suitable for applications where detecting the smallest features is critical. These lenses achieve superior resolution through advanced optical designs that minimize aberrations and maximize contrast.

Conversely, the large depth of field versions are engineered to maintain sharp focus across a more extensive range of object distances. This is particularly beneficial in scenarios where the object has significant depth variations or when the imaging system must accommodate parts with different heights without mechanical adjustments. The depth of field in these versions is typically about twice that of the high-resolution versions, achieved through carefully controlled aperture settings and specialized lens coatings that manage light transmission and reduce diffraction effects. The ability to choose between high-resolution and large depth of field versions allows users to select the lens that best fits their specific inspection requirements. In industries such as electronics manufacturing, where components can have intricate patterns and varying thicknesses, having this flexibility is invaluable. For instance, in printed circuit board (PCB) inspection, high-resolution lenses can detect micro-cracks or soldering defects, while large depth of field lenses ensure that all layers of multi-layered boards are in focus simultaneously.

Basson’s commitment to optical excellence extends beyond lens design to the overall performance and reliability of their products. Their telecentric and bi-telecentric lenses are built with high-quality materials and precision manufacturing processes to ensure consistent performance in demanding industrial environments. Coatings are applied to lens elements to enhance light transmission, reduce reflections, and improve image contrast, further supporting the lenses’ ability to deliver clear, detailed images under various lighting conditions. Moreover, Basson lenses are designed with ease of integration in mind. They are compatible with a wide range of cameras and imaging systems, making them versatile tools for different inspection setups. The robust mechanical design ensures stability and durability, which is critical in automated systems where lenses are subject to continuous operation and potential exposure to harsh conditions.

While the physical principles of optics impose certain limitations on simultaneously achieving both high object space resolution and a large depth of field, Basson’s telecentric and bi-telecentric lenses offer optimized solutions tailored to specific needs. By providing high-resolution versions for detail-critical inspections and large depth of field versions for applications requiring consistent focus across varying object depths, Basson ensures that customers have the right tools to meet their inspection challenges. This combination of advanced optical design, high-quality manufacturing, and application-specific optimization makes Basson an excellent partner in the field of visual inspection, capable of addressing a wide range of industrial imaging requirements.

Basson’s telecentric and bi-telecentric lens systems exemplify the harmonization of optical theory and practical engineering. By fundamentally rethinking the relationship between aperture control, diffraction management, and optical path optimization, they deliver unprecedented combinations of resolution and depth performance. This technological achievement not only addresses current industrial imaging challenges but also creates new possibilities in scientific research and quality assurance methodologies. As manufacturing tolerances tighten and inspection requirements grow more complex, Basson’s optical solutions stand poised to redefine industry standards, offering engineers and researchers alike the tools to visualize and measure our world with unparalleled precision and reliability.

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.