Telecentric illumination

Telecentric illumination is needed in a wide variety of applications including:

• High speed inspection and sorting: in fact, when coupled with a telecentric lens, the high throughput allows for extremely short exposure times
• Silhouette imaging for accurate edge detection and defect analysis
• Measurement of reflective cylindrical objects: diffuse backlights can generate undesired reflections from the edges of shiny round objects, making them look smaller than they are and leading to inaccurate measurements. Since collimated rays are typically much less reflected, telecentric illuminators can effectively eliminate this “border effect” ensuring accurate and consistent readings

Any precision measurement application where accuracy, repeatability and high throughput are key factors.

The use of a collimated light in combination with a telecentric lens increases the natural depth of field of the telecentric lens itself by approximately +20/30% (this however also depends on other factors such as the lens type, light wavelength and pixel size).

Additionally, thanks to the excellent light coupling, the distance between the object and the light source can be increased where needed without affecting image quality. This happens because the illuminator’s numerical aperture (NA) is lower than the telecentric lens NA.

Therefore, the optical system behaves as if the lens had the same NA as the illuminator in terms of field depth, while maintaining the same image resolution given by the actual telecentric lens NA.

Collimated light is the best choice if you need to inspect objects with curved edges; for this reason, this illumination technique is widely used in measurement systems for shafts, tubes, screws, springs, o-rings and similar samples.