Coaxial lighting
Coaxial lighting is diffuse incident light or bright field lighting. The light of an LEDsurface illumination is coupled laterally via a semi-transparent mirror into the beam path of a camera and projected onto the test object. This ensures that the test object is illuminated very evenly and without shadows. The light from the test specimen then passes through the semi-transparent mirror to the camera.
Coaxial lighting is ideal for highly reflective or translucent materials with a fairly flat surface. Unevenness in the surface deflects the light to the side and appears dark, e.g. scratches, embossed characters and edges.
How coaxial lighting works (source: Vision Doctor).
Notes:
– The ideal working distance is as short as possible, just a few centimeters.
– The light field should be significantly larger than the object to be tested.
– It should be noted that 50% of the light is lost at each transition through the semi-transparent mirror, so that only 25% of the original amount of light reaches the camera.
Comparable diffuse incident lighting systems are tunnel lighting and dome lighting.
