Telecentric Lens - Shenzhen Yixian Sensing Technology Co., Ltd

Telecentric Lens
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Telecentric Lens FAQs

What Is a Telecentric Lens? What’s the Difference from a Standard Lens?

A telecentric lens is a specialized optical lens. Classified by its optical structure into object-side telecentric, image-side telecentric, and double-sided telecentric lenses, its core feature is that the principal rays propagate parallel to the optical axis. Taking the object-side telecentric lens as an example: its entrance pupil is located at infinity. Even if the object moves along the optical axis within a certain depth of field range, the imaging magnification remains almost unchanged—a trait that enables telecentric lenses to excel in measurement accuracy.

The core difference between telecentric lenses and standard lenses lies in their imaging characteristics:

Standard lenses have parallax. When the object is at different distances from the lens, the imaging size changes, which leads to measurement errors. For instance, using a standard lens to measure a mechanical part may result in an overestimated or underestimated size if the part shifts slightly closer to or farther from the lens.
Telecentric lenses, through special optical design, achieve nearly parallel propagation of principal rays. This greatly reduces or even eliminates parallax, ensuring the imaging size of the object remains consistent at different distances. Thus, in high-precision measurement and inspection scenarios where dimensional accuracy is critical (e.g., semiconductor chip size measurement, precision part inspection), telecentric lenses have incomparable advantages.

How to Select a Suitable Telecentric Lens Based on Camera Pixels?

Camera pixels determine the image’s detail-capturing capability. When selecting a telecentric lens, it is essential to ensure the lens’s resolution matches the camera’s pixel resolution.

In general, the lens resolution should be higher than the camera’s pixel resolution. This is because if the lens resolution is insufficient, it will become the "bottleneck" of the imaging system—even a high-pixel camera cannot capture clear details, resulting in blurry images and compromised measurement accuracy.

For example, for a high-pixel industrial camera (e.g., 20 million pixels or more), a high-resolution telecentric lens (with a resolution typically corresponding to or exceeding the camera’s pixel density) should be paired. This ensures that the lens can fully transmit the fine detail information captured by the camera’s pixels, avoiding image blurring caused by insufficient lens resolution and maximizing the camera’s pixel advantages to achieve precise imaging and measurement.

Why Can Telecentric Lenses Achieve High-Precision Imaging?

Telecentric lenses adopt a telecentric optical path design:

For an object-side telecentric lens, the aperture stop is located on the image-side focal plane;
For an image-side telecentric lens, the aperture stop is located on the object-side focal plane;
A double-sided telecentric lens combines the characteristics of both.

This design ensures that the principal rays propagate parallel to the optical axis. During imaging, the light is barely affected by changes in the object’s position (e.g., slight shifts along the optical axis within the depth of field). As a result, the lens delivers high resolution and low distortion, accurately restoring the object’s true size and shape—ultimately enabling high-precision imaging.

How to Choose Between Object-Side Telecentric Lenses, Image-Side Telecentric Lenses, and Double-Sided Telecentric Lenses?

Object-side telecentric lenses are suitable for scenarios where high precision in object size measurement is required, and the object position varies to a certain extent in the object-side space. They can ensure that the imaging size of the object remains consistent even when the object is at different positions.
Image-side telecentric lenses are often used in situations where the position of the imaging plane changes, and a stable image height is needed.
Double-sided telecentric lenses combine the advantages of the two aforementioned types. They are applicable to scenarios that are sensitive to changes in both object distance and image distance, and have extremely high requirements for imaging precision—such as high-precision wafer inspection.

In actual selection, the specific inspection task and working environment should be taken into account to determine the appropriate type of telecentric lens.

What Impact Does the Distortion Rate of a Telecentric Lens Have on Inspection Results?

Telecentric lenses feature an extremely low distortion rate, which is almost negligible—and this is a key advantage for their use in high-precision inspection.

Low distortion ensures that the imaged shape of an object is highly consistent with its actual shape, preventing deviations in inspection results caused by lens distortion.

For example, in the contour inspection of precision parts: if a lens has a high distortion rate, the part’s contour will be deformed in the image. This deformation directly impairs the accuracy of dimensional measurement (e.g., incorrect readings of length, diameter, or angle) and defect judgment (e.g., misidentifying normal contour variations as defects or failing to detect real flaws). In contrast, the low-distortion characteristic of telecentric lenses effectively avoids such issues, ensuring that inspection data truly reflects the object’s actual state.

How Does a Telecentric Lens Perform in Terms of Imaging Under Different Lighting Conditions?

Telecentric lenses have a certain degree of adaptability to lighting conditions, but the uniformity and intensity of light will affect imaging quality.

Under uniform and stable lighting, telecentric lenses can produce clear images with high contrast, which is conducive to accurate observation and measurement of object details.
If the lighting is non-uniform, it may cause local over-brightness or over-darkness in the image, obscuring fine details of the object and thus affecting the precision of inspection and measurement.
When the light intensity is insufficient, the image will be dark and the signal-to-noise ratio will decrease, leading to blurred edges of the object and reduced accuracy of dimensional measurement.

Therefore, in practical applications, it is usually necessary to match the telecentric lens with a suitable lighting system (such as coaxial light sources or ring light sources) to ensure uniform light distribution and appropriate intensity, thereby enabling the telecentric lens to achieve the best imaging effect.

Can Telecentric Lenses Be Used for Dynamic Object Inspection?

Telecentric lenses can be used for dynamic object inspection, but it is necessary to consider the matching between the object's movement speed and the camera's frame rate.

If the object moves too fast while the camera has a low frame rate, it may cause image motion blur, which impairs inspection accuracy. In such cases, a high-frame-rate camera should be selected, and the exposure time should be adjusted reasonably according to the object's movement speed. At the same time, it is essential to ensure that the lens's resolution and imaging quality can still meet the inspection requirements under dynamic conditions.

What Solutions Do Telecentric Lenses Offer for Large-Size Object Inspection?

For the inspection of large-size objects, a single telecentric lens may not be able to cover the entire object. In such cases, the following solutions can be adopted:

First, a multi-telecentric lens stitching method can be used. Images captured by multiple telecentric lenses are stitched together via software algorithms, enabling complete inspection of large-size objects.

Second, a wide-field-of-view telecentric lens can be selected. However, wide-field-of-view lenses may have trade-offs in aspects like resolution, so a balance needs to be struck between the field of view and inspection accuracy.

Additionally, a regional inspection method can be implemented by moving the lens or the object itself, allowing the large-size object to be inspected in separate regions.