Angle of illumination
There are two major lighting areas as shown in the diagram, 'front lighting' where the light originates from the same side as the camera, and 'backlighting', where the light source is situated behind the target.
The techniques are summarised below:
Front light illumination:
- Coaxial illumination (including advanced coaxial and collimated coaxial illumination)
- Special diffuse illumination techniques (for example flat dome illumination)
- Bright field illumination
- Dark field illumination
- Transmissive and collimated backlight illumination
- Bright field backlight illumination
- Dark field backlight illumination (for transparent objects)
To understand the terms bright field and dark field, we replace the test object by a perfect plain mirror. Bright field refers to any illumination where the light rays from the source are reflected from the mirror directly into the lens. Dark field refers to any illumination where the light rays are not reflected into the lens, but only a proportion of light that is scattered by an uneven surface.
These main illumination techniques can be achieved using different products.
More illumination methods: