Common Illumination Techniques in Metallurgical Microscopy
① Direct Illumination: Light shines directly onto the object to form a clear image. It works well when high contrast is required. However, when applied to bright or reflective specimens, specular reflection will occur.
② Darkfield Illumination: Light hits the specimen surface at an oblique angle. Oblique scattered light enters the objective, creating bright features against a dark background. If the specimen surface has no color difference, it cannot be distinguished by the optical system. These two illumination modes are commonly equipped on metallurgical microscopes.
③ Backlight Illumination: Uniform light shines from the rear side of the specimen. The microscope captures the contour profile of the object. Backlight illumination is used for measuring specimen dimensions and determining orientation.
④ Diffuse Reflection Illumination: It provides non-directional light, similar to soft shadowless light. This lighting is suitable for highly reflective objects. Its effect resembles soft, non-directional light on an overcast day.
⑤ Coaxial Illumination: A coaxial light source emits light along the vertical direction. The light passes through a 45° half‑mirror and irradiates the object vertically. This type of illumination is especially helpful for inspecting highly reflective surfaces.
