Briefly describe the principle of bi-telecentric industrial lens

Understanding Double Telecentric Lenses in Machine Vision

In recent years, terms like single-sided telecentric, object-space telecentric, image-space telecentric, and double-sided telecentric have gained prominence in machine vision, especially in precision measurement. These optical concepts might be complex, but understanding their basic principles can be beneficial in real-world applications.

Double Telecentric Lenses: An Overview

Convex Lens Imaging Principle A convex lens has two key characteristics:

1. All rays passing through the optical center do not change their propagation direction.
2. Convex lenses converge parallel rays, which is a key aspect of how lenses create images.

Double Telecentric Lens Principle A double telecentric lens has an aperture in the middle, allowing only parallel light rays to enter and exit the lens, while other rays are blocked by the aperture. This feature creates both object-space and image-space telecentricity.

• Object-Space Telecentric Lens: This type addresses depth of field issues, allowing consistent focus over varying distances.
• Image-Space Telecentric Lens: This type maintains constant magnification, eliminating changes in magnification with different distances.

A double telecentric lens combines the advantages of both, resolving common problems encountered with traditional industrial lenses.

Problems Addressed by Double Telecentric Lenses

1. Resolution: Traditional industrial lenses often can't keep up with increasing camera sensor resolutions, typically capping at about 10 micrometers. Double telecentric lenses can work with high-resolution cameras, meeting current high-precision measurement requirements.

2. Depth of Field: Regular lenses have a smaller depth of field, which can lead to incomplete measurements when objects extend beyond this range. Double telecentric lenses, with their broader depth of field, resolve this issue.

3. Magnification: Regular lenses can change magnification with varying distances, introducing errors in precision measurement tasks. Double telecentric lenses maintain constant magnification, eliminating this issue.

Characteristics of Double Telecentric Lenses

Double telecentric lenses are generally larger in size because they require larger barrels to accommodate the parallel light path. This size increases with a broader field of view.

When choosing a double telecentric lens, it's essential to consider the field of view, compatible CCD sensor size, and interface type. Additional factors like working distance and shape are less critical as long as they don't affect usability.

Due to the reliance on parallel light, double telecentric lenses often require dedicated light sources, as they filter out most diffuse reflected light, resulting in darker images in natural environments. Parallel light sources can maximize the advantages of double telecentric lenses, providing clear and stable edge detection while reducing noise in the measurement process.