[erdmann]

Yes, because the surface isn't flat. At these magnifications, any given field of view may be tilted toward one of the light sources, changing the relative contribution of the specular reflection off of the varnish as well as the reflected color from the paint surface. The apparatus doesn't have the ability to tilt to maintain a constant angle to the surface; it can only pan in the x-y plane and do focus stacking in the z-direction. Additionally, the left and right light sources were hand-positioned and there is no way to calibrate their exact geometry and relative brightness and color.

[jahlove]

thanks for explaining!