Differences in appearance between coaxial illumination and ring illumination.

Depending on the object, some are suitable for coaxial illumination, while others are more appropriate for ring illumination.

However, ring illumination is more versatile.

Coaxial illumination can only be used for objects that are “glossy” and “flat.”

■Features of Coaxial Illumination




Coaxial illumination is a suitable method for objects with specular reflection (glossy surfaces).

When oblique light, such as from ring illumination, is directed at a specular object, it reflects at the same angle as the incident angle, preventing light from returning to the lens and resulting in a dark image.

However, coaxial illumination is not suitable for glossy objects with uneven surfaces or curvature.

When used on diffusive reflective objects, coaxial illumination causes only the central part to become bright (hotspot), resulting in a foggy image without color contrast.



サンプル1   基板の金メッキ部分





The illumination method of a metallurgical microscope (coaxial illumination) is designed for nearly mirror-like, flat objects.

The appearance can significantly differ compared to conventional illumination (ring illumination).

サンプル2   1円玉





White and black completely invert.

(The closer the surface is to a mirror finish, the more pronounced this effect becomes.)



サンプル3  銀メッキのコイン





A silver-plated coin, like the one in the above photo, can be observed with both coaxial and ring illumination.

(Since it is not a perfect specular reflector, both methods are suitable.)



Sample 4: 10-yen coin (diffuse reflector)




A 10-yen coin cannot be observed with coaxial illumination.



Sample 5: Circuit board (observation of diffuse reflector)




Diffuse reflectors cannot be observed with coaxial illumination.



Sample 6: Observation of specular reflectors





Perfect specular reflectors (those close to mirror surfaces) cannot be observed with ring illumination.



Sample 7: Nickel processed product






When using coaxial illumination, please note that diffuse objects cannot be observed.

(Even with metals, black anodizing or paint may be better observed with ring illumination.)



Sample 8: Paper (printed material)





Sample 9: Other objects unsuitable for coaxial illumination