Solution (3)] Shomei problem

This is a continuation of my previous post.

1. the image obtained when coaxial lighting was used?

As follows.

Because the areas that have been rubbed and made smooth are almost mirrors,

Direct light by coaxial illumination is,

Hit the rubbing area,

It is captured by the camera as it is.

(90 degrees angle of reflection for 90 degrees angle of incidence.)

Therefore, the scuffed area will be white.

2. consider also the case of small ring lighting (high angle).