Opto-Engineering Coaxial light provide highly diffuse illumination by providing the same optical axis for both the camera and the light source.  This type of light is also commonly known as Diffuse On-Axis Lighting.

The highly diffuse nature of the light field renders this type of illumination ideal for imaging highly specular shiny surfaces. For example, a metal coin can return direct powerful reflections, the most challenging of which is cause by metallic curved surfaces that focus ambient light into a small intense specular highlight.