What Is a Telecentric Lens?
Color-Changing at High Temperatures
A telecentric lens is a special type of lens designed with an optical axis that runs parallel to the principal ray. This design allows for capturing images without angular view or parallax error. It’s particularly effective for objects with uneven surfaces or depth, ensuring constant magnification, ideal for precision processing.
These lenses are adept at producing distortion-free images, maintaining consistency across the center and edges. They are commonly used for inspecting minute surface details like scratches and dust on reflective objects, including glass.
Applications of Telecentric Lenses
Telecentric lenses have diverse applications, such as in the inspection of three-dimensional objects. They prevent the distortion typical in images captured with normal lenses, ensuring an accurate representation of the object. This makes them valuable for detecting dust and scratches, as their design helps avoid errors due to parallax, enhancing the visibility of such imperfections.
Types and Principles of Telecentric Lenses
- Object-side Telecentric Lenses: These lenses have parallel main rays on the object side, enabling accurate measurement without size alteration due to object movement. They are relatively compact.
- Image-side Telecentric Lenses: Positioned on the image side, these lenses maintain uniform brightness on the image plane, although the image size may vary with object movement.
- Bilateral Telecentric Lenses: Utilizing two lenses, these offer parallel main rays on both object and image sides, providing enhanced accuracy.
Limitations of Telecentric Lenses
Telecentric lenses tend to have a large diameter, dictated by the CCD/CMOS element size. While suitable for small objects, their large size can be a constraint in space-limited applications. They are also not ideal for systems that require depth information, like VR and AR, due to their inability to capture depth via binocular parallax.
Calibration and Performance of Telecentric Lenses
While telecentric lenses minimize errors caused by the angle of view, they are not free from distortion. Common optical distortion is around ±0.5%, which is lower than typical lenses (±20% or more). It’s crucial to consider this in applications where even minor distortion impacts performance, requiring additional software or hardware correction.