Vision Optical Engineering: Why Telecentric Lenses?

  • Vision & Optics

A Vision project is 30% software, 70% hardware. Even the world's best AI cannot salvage a photo taken with the wrong lens and lighting.

1. The Perspective Error (Parallax)

Standard (Entocentric) lenses see like the human eye: Objects further away appear smaller. This is good for photography but catastrophic for metrology.

If you measure a 5mm tall nut, a standard lens sees both the top surface and the side walls. Thus, the diameter you measure is not the "true diameter".

2. The Solution: Telecentric Lenses

Telecentric lenses only accept light rays parallel to the optical axis. The result?

  • Object size does not change with distance (Magnification constancy).
  • You do not see the side walls of holes or pins, only the perfect top cross-section.
  • Mandatory for micron-level (±0.005mm) precision measurements.

3. Importance of Wavelength

Why do Vision systems use Red (630nm) or Blue (465nm) light?

  • Short Wavelength (Blue): Provides higher resolution (Diffraction limit). Reveals micro-scratches on metal surfaces better.
  • Long Wavelength (Red/IR): High penetration. Ideal for seeing "through" oil or dirt, or contrasting specific colored inks.