In the field of industrial inspection, quality control for deep-hole and groove-type workpieces has always been a challenging task. Such inspections not only demand extremely high precision but are also often constrained by the inherent characteristics of the workpieces themselves, making it difficult for traditional inspection methods to achieve ideal results. Telecentric lenses, with their unique optical design, have emerged as the key solution to overcoming these challenges.

Challenges in inspecting deep holes (such as blind holes and through holes in mechanical parts) and grooves (such as retaining slots in electronic components and precision component grooves):

1. Image distortion is severe.：Conventional lenses suffer from perspective distortion. When inspecting the inner walls of deep holes or the bottoms of grooves, the inclined angle of light easily causes edge distortion and dimensional imbalance, directly compromising measurement accuracy.

2. Internal details are difficult to grasp.：When deep holes have significant depth or grooves are particularly deep, the limited depth of field of standard lenses makes it difficult for light to adequately illuminate the interior. This results in blurred or even unimageable details at the bottom or on the inner walls.

3. The conflict between ultra-high precision requirements and minute dimensions：Many products under inspection—such as the inner bores of miniature bearings or grooves in semiconductor chips—feature extremely small dimensions (potentially only a few millimeters or even micrometers). Yet the required inspection accuracy often demands micrometer-level precision, which traditional lenses struggle to achieve due to limitations in resolution and stability.

4. Reflective interference is significant.：When the surface roughness of the test object is high (such as deep holes in castings or stampings), intense diffuse or specular reflections occur after light exposure. This results in bright spots or glare in the image, obscuring actual defects like scratches or burrs.

Telephoto Lens Solutions: Addressing Pain Points Through Feature-Based Approaches

Telecentric lenses (including object-side telecentric, image-side telecentric, and dual-side telecentric) employ a specialized optical design that positions the aperture diaphragm at the focal point of the optical system. This configuration delivers a range of advantages for precision inspection, specifically addressing the challenges of deep hole/groove inspection:

1. Low distortion, no image distortion：Telecentric lenses typically maintain distortion rates below 0.1%, or even lower. Whether inspecting the side walls of deep holes or the corners of grooves, they preserve true geometric shapes, ensuring accurate dimensional measurements (such as aperture, groove width, and depth) and preventing misjudgments caused by distortion.

2. Magnification remains constant regardless of object distance.：For positions at varying depths within deep holes or the upper and lower edges of grooves, telecentric lenses maintain consistent magnification ratios, enabling precise inspection across the entire area without additional calibration. They are particularly well-suited for scenarios requiring measurement of depth or step height.

3. Depth-of-field optimization, adapted for depth-structured layouts：By combining appropriate light sources and optical parameters, telecentric lenses deliver a greater depth of field range, ensuring clear imaging of details at the bottom of deep holes and within recesses, thereby resolving the issue of “invisible interiors.”

4. Enhanced anti-reflective capability：When paired with coaxial or annular low-angle light sources, telecentric lenses minimize stray light interference from rough surfaces, enabling clearer visualization of workpiece edges and internal defects such as cracks and pits. This reduces missed inspections caused by reflections.

Image Display: