gj
Interpreting the Ronchi Shadows from your mirror can be confusing at times. Using information found on the internet and in telescope making books, I created a small webpage showing various pictures of ronchi shadows and their corresponding surface defects.

I initially put this together for myself, to have an overview of various possible ronchi shadows, but I decided to put this on the web for anyone to enjoy.

Note: The surface drawings displayed here are meant to give you a general idea of the relationship between the ronchi shadows and the mirror's surface. They are not highly accurate to-scale drawings of the mirror.

Also note that what's shown in the surface drawings is the deviation from a spherical surface. In other words, a spherical surface would show as a flat surface in the drawings. The Ronchi shadows for a spherical mirror are straight lines.

Shadow Outside RoC Inside RoC
shadow surface
(Overcorrected)
surface
(Undercorrected)
shadow surface
(Overcorrected)
surface
(Undercorrected)
shadow surface
(Undercorrected)
surface
(Overcorrected)
shadow surface
(Depressed ring)
surface
(Raised ring)
shadow surface
(Central hole)
surface
(Central bump)
shadow surface
(Undercorrected)
surface
(Overcorrected)
shadow surface
(Undercorrected)
surface
(Overcorrected)
shadow surface
(Overcorrected)
surface
(Undercorrected)
shadow surface
(Raised ring)
surface
(Depressed ring)
shadow surface
(Central bump)
surface
(Central hole)
Credits
I didn't create the Ronchi shadow images myself. I copied them from a web page created by Richard Ozer. The surface drawings are created by me.
MacRonchi 2.0
MacRonchi icon

Compare the ronchi lines on your mirror with the shadows of a perfect mirror with MacRonchi 2.0, my free Mac OS X application for simulating the ronchi test.
More on Ronchi Testing


Copyright (C) 2002, Gert Jan Verhoog. Last Modified 03/27/2002, 21:18:59