Selection Parameters of Telecentric Objectives and Their Advantages in Large Workpiece Measurement Applications

Parameters for Selecting Telecentric Objectives

Resolution

The sensor of the camera consists of many pixels arranged in a matrix. Resolution is represented by the number of pixels in the horizontal and vertical directions. The higher the resolution, the higher the number of pixels in the image and the clearer the image. Common resolutions for industrial area cameras are 1.3 million, 2 million, 5 million, etc. For line scan cameras, resolution is the number of pixels in the horizontal direction of the sensor, commonly 2K, 4K, 8K, etc. 

The selection of camera resolution should be based on the requirements of our project; higher resolution is not always better, as it comes with larger image data volume and higher complexity in post-processing algorithms. Furthermore, cameras with higher resolutions generally do not have high frame rates.

Sensor Size

Sensor size is represented by its effective area (width x height) or by its diagonal size (in inches). A larger sensor size generally means the camera can accommodate more pixels and produce larger image formats.

Telecentricity

The ability of telecentric objectives to eliminate perspective errors varies among manufacturers, due to differences in telecentricity. For measurements involving non-planar objects, only telecentric objectives with high telecentricity can effectively eliminate perspective errors, thereby reducing measurement errors.

Depth of Field

Depth of field is a crucial parameter in optical photography, determining the range within which the image appears sharp. In telecentric optical imaging, depth of field is also frequently mentioned. It is influenced by lens magnification, aperture number, wavelength, pixel size, and the sensitivity of the edge extraction algorithm used by the customer. Depth of field is important for measurement applications, typically greater than the depth of field required for defect detection, and the image contrast should be as high as possible. 

Depth of field is difficult to define parametrically: it depends on magnification, aperture number, wavelength, pixel size, and the sensitivity of the edge extraction algorithm. Therefore, there is no objective or standard way to define it, as it is a subjective parameter. Depth of field = (working aperture number * pixel size * application-specific parameters) / (magnification * magnification).

Advantages of Telecentric Objectives in Large Workpiece Measurement Applications

Telecentric industrial lenses are optical devices with excellent image quality and precision, widely used in the measurement and inspection of large workpieces. Compared to ordinary industrial lenses, telecentric objectives have the following advantages:

First, in the measurement of large workpieces, a large field of view and depth are required to cover a wider measurement range and ensure the accuracy of measurement results. Telecentric objectives can provide a larger field of view and depth, allowing for comprehensive and efficient measurements without moving the workpiece and without affecting the measurement results.

Second, telecentric objectives have better resolution and aberration control, effectively eliminating image distortion, chromatic aberration, and distortion while ensuring measurement accuracy. This makes telecentric objectives particularly suitable for high-demand industrial measurement tasks, such as high-precision mold measurement and automotive body measurement.

Additionally, telecentric objectives feature large apertures and high luminous flux, which allow more light to enter the lens, thereby increasing the brightness and signal-to-noise ratio of the entire system. This is significant for measurement applications in darker environments, such as measuring black materials or materials with uneven surfaces.

Overall, telecentric objectives are one of the important optical devices in the measurement of large workpieces and play an irreplaceable role in many fields. Their excellent image quality and precision can improve work efficiency and reduce work intensity while ensuring measurement accuracy, thus contributing to the advancement and development of industrial production and quality assurance.