What is the difference between a telecentric lens and a normal lens?

In machine vision applications, there is a significant difference between standard lenses and telecentric lenses. Telecentric lenses are specifically designed to correct parallax, allowing them to maintain a constant magnification regardless of the object distance within a certain range. This is crucial when the objects being measured are not on the same plane, preventing the "near large, far small" phenomenon.

Issues with Standard Industrial Lenses

When using standard industrial lenses for measurement, there are several issues that can occur:

1. Varying Magnification: The closer the object is to the lens, the larger the image becomes, causing discrepancies when objects are at different distances.

2. Lens Distortion: Standard lenses can have significant distortion, affecting the accuracy of measurements.

3. Parallax: When object distances change, the magnification also changes, leading to inconsistencies in measurements.

4. Lower Resolution: Standard lenses may not offer high enough resolution for precise measurements.

5. Uncertain Edge Detection: Due to the geometry of the lighting source, standard lenses can produce images with uncertain edge positions, making measurement less reliable.

Advantages of Telecentric Lenses

Telecentric lenses address the above issues effectively, making them ideal for high-precision measurement and metrology applications. These lenses maintain constant magnification, eliminating parallax, and offer high image quality. Their unique parallel light design is particularly useful for capturing consistent images regardless of object distance or orientation.

Comparisons between Telecentric and Standard Lenses

Here are a few comparisons demonstrating the benefits of telecentric lenses over standard lenses:

Capturing Small Holes

With standard lenses, visual focus errors can cause shadows and unclear inner wall edges, affecting the extraction of edge details. This can lead to lower accuracy in measuring small holes.

With telecentric lenses, the unique parallel light design ensures sharp, clear outlines, providing accurate data without excessive image correction.

Capturing Gears

Standard lenses may introduce visual distortion, making it challenging to obtain accurate gear measurements. The gear's central hole might show visual artifacts due to parallax, requiring complex correction algorithms.

Telecentric lenses, with their parallel light path, deliver clear and accurate images without parallax, making the inner and outer edges of gears sharp and precise, eliminating the need for correction.

Capturing Molds

Standard lenses may result in focus errors and shadows when capturing mold details like vent holes, affecting the precision of data extraction.

Telecentric lenses, with their consistent parallel light path, offer clear edge detection and accurate data for both vent holes and mold measurements, reducing errors and simplifying inspection.

Pros and Cons of Telecentric Lenses

• Advantages:

  • Stable magnification that doesn't change with depth of field.
  • No parallax.
  • Low distortion.
  • Ideal for precise measurements.

• Disadvantages:

  • Higher cost.
  • Larger size and heavier weight.

Applications for Telecentric Lenses

Telecentric lenses are well-suited for measuring precise components in industrial and metrology applications where consistency, accuracy, and low distortion are crucial. Their unique design allows for accurate measurements across a range of distances, making them invaluable in high-precision environments.