What are the advantages of telecentric lenses over ordinary lenses?

In machine vision applications, there are regular lenses and telecentric lenses. The key difference is that telecentric lenses are specifically designed to correct the parallax effects of traditional industrial lenses. Telecentric lenses maintain a consistent magnification within a certain range of object distance, preventing the "closer is bigger" effect. This is especially important in applications where objects are not on the same plane.

Regular industrial lenses, however, exhibit a characteristic where objects appear larger the closer they are to the lens (shorter working distance). When using regular lenses for dimensional measurement, the following issues may arise:

1. Different magnifications: Due to the measured object not being on the same measurement plane, the magnification may vary.
2. High lens distortion: Regular lenses often have noticeable distortion.
3. Parallax: Magnification changes with object distance, leading to variable scaling.
4. Low resolution: Regular lenses may not capture high-resolution images.
5. Uncertainty in edge positions: Due to the geometric properties of visual light sources, the edges in the image may be imprecise.

Telecentric lenses can effectively solve these issues and avoid such parallax-induced errors, making them suitable for high-precision measurements and metrology applications. They are a type of high-end industrial lens known for exceptional image quality, with minimal distortion, making them ideal for size measurement applications. Double-sided telecentric lenses offer even greater advantages.

Telecentric Lenses and Regular Lenses: Comparison in Photography

1. Shooting Small Holes

With regular lenses, parallax errors can lead to shadows on the inner walls of small holes, affecting edge extraction and reducing image accuracy. Using a telecentric lens with a continuous zoom, thanks to its unique parallel light characteristic, ensures a clear outline of the small hole without requiring extensive image corrections.

2. Shooting Gears

Regular industrial lenses, due to non-parallel light paths, create visual errors. The resulting images might show visible inner walls of gear holes, with the entire gear appearing convex, leading to inaccurate data for hole diameter and edge measurements, necessitating complex correction algorithms. Telecentric lenses, with their parallel light path design, ensure a clear and accurate depiction of the gear's outer and inner edges without distortion, eliminating the need for image correction.

3. Shooting Molds

With regular lenses, visual errors and imprecise focus can cause shadows and unclear edges when photographing ventilation holes in plastic molds, impacting identification and data accuracy. Telecentric lenses, owing to their parallel light characteristic, produce clear inner wall edges and precise data. When photographing circular holes, the edges are clear, making it easier to detect burrs and measure hole diameters.

Advantages and Disadvantages of Telecentric Lenses vs. Regular Lenses

Regular Lenses

• Advantages: Low cost, versatile, and widely applicable.
• Disadvantages: Variable magnification, presence of parallax.
• Applications: Magnifying objects and imaging.

Telecentric Lenses

• Advantages: Constant magnification, unaffected by depth of field changes, no parallax, and low distortion.
• Disadvantages: High cost, large size, heavy weight.
• Applications: Precision measurement of fine parts.