In What Situations Is a Telecentric Lens Needed?

Telecentric Lenses play a crucial role in the fields of machine vision and industrial inspection. Their design primarily aims to address the parallax issues present in traditional industrial lenses, thereby maintaining consistent image magnification within a certain range of object distances. Understanding when to use telecentric lenses can help you perform product inspections and measurements more effectively.

Core Functions of Telecentric Lenses

Telecentric lenses aim to correct the parallax effect present in traditional industrial lenses, thereby maintaining consistent image magnification over a certain distance. For general surface defect detection or simple presence/absence judgments of objects, choosing a low-distortion FA lens is usually sufficient. However, in the following scenarios, telecentric lenses become particularly important.

Inconsistent workpiece angles

In visual inspections, it is often difficult to align the workpiece coaxially with the camera, resulting in parallax and distorted edge contours. Using telecentric lenses effectively solves this issue, ensuring clear imaging.

Magnification inconsistency due to distance variations

When the distance between the workpiece and the camera cannot be maintained consistently, the magnification of the workpiece in the image will vary. Telecentric lenses can maintain consistent magnification at different distances, ensuring measurement accuracy.

Insufficient depth of field

Regular lenses have limited depth of field, resulting in uneven image clarity across different depth regions of the workpiece. The design of telecentric lenses allows them to provide clear images over a larger depth of field range.

High distortion problems

Traditional lenses cause deformation in the images of workpieces due to varying degrees of distortion in the center and edge areas. The special design of telecentric lenses significantly reduces the impact of this issue.

Inspection of transparent or reflective materials

Some transparent materials (such as glass, acrylic) or reflective materials (like metal, smooth glass) present challenges in capturing clear edge contours with conventional lenses. Telecentric lenses can effectively capture the details of these materials.

Classification of Telecentric Lenses

In precision measurement and visual inspection systems, choosing telecentric lenses can overcome perspective differences, ensuring that the dimensional data obtained during object movement remains almost unchanged. Telecentric lenses are mainly divided into the following three types:

Object-side telecentric lenses

This type of lens only receives parallel light for imaging, equivalent to the object being at infinity. Even if the object distance changes, the image height will not change, thereby keeping the measured object size consistent.

Image-side telecentric lenses

Only light parallel to the optical axis can pass through this lens to reach the front of the CCD/CMOS sensor, thereby avoiding the occurrence of shadows. This feature allows it to provide clear images even under poor lighting conditions.

Double-sided telecentric lenses

Combining the advantages of object-side telecentric lenses and image-side telecentric lenses, double-sided telecentric lenses can receive parallel light from multiple directions, ensuring the consistency of image quality.

In machine vision and industrial inspection, telecentric lenses are effective tools for solving various imaging problems. Whether facing complex workpiece shapes, varying shooting distances, or scenarios requiring high-precision measurements, telecentric lenses provide reliable solutions. By understanding the core functions and suitable occasions for telecentric lenses, you can better select the lenses that meet your application needs, thereby improving inspection efficiency and image quality.