About Micrometers

All transmitted light versions are produced as a positive image, so opaque lines on a clear background. When the light is transmitted through the stage micrometer the scale image will appear with dark lines against a bright background. This is because no light can pass through the opaque lines, so they appear black. When you use the same transmitted light stage micrometer on an incident/reflected light microscope, the light is reflected by the chrome lines but passes through the clear areas, thus the image will appear with bright lines against a dark background. Because the light also has some reflectance from the edges of the lines, the scale will appear very slightly less defined than when it is used with transmitted light. The same will apply when a reflected light stage micrometer is used for transmitted light (all reflected light versions have clear lines on an opaque background). Does that make sense?!

More information by Pyser/Gradicules Optoics (PDF):

Handout Stage Micrometers

Guide - Micrometers

Practical example by Science Services:

Measuring the thickness of a coating on leather by using a microscope, reticle, digital camera and software.

Instruction how to measure with a Microscope (PDF)