A Slitless Ronchi Tester Using a Film Grating

Film used for printed circuit board manufacturing is very well suited for making gratings and other fine structures to be used in a tester for telescope optics. The film has the following advantages For the Ronchi gratings a Postscript file is used that can be directly fed into the optical printing machine. For example a pattern of 12black pixels and 12clear pixels equals a grating of 100lpi. Once defined in the Postscript file the pattern can be drawn in any size matching the requirement of a given tester.

As mentioned not only Ronchi gratings can be manufactured that way. Knife edge as well as wire tester patterns are easily doable as well.

Here my tester setup with a small digital camera to take the Ronchi pictures.
The light source is a bright white LED with a flattened front surface behind a ground piece of glass.

Here a close-up of the optical head of the tester with a Foucault pattern installed.

Here is a Foucault image using the above setup.


Here the same with a Ronchi grating. The tester is in slitless mode of operation.
The light source is behind the same grating as the observer.


The last batch of film seems to show a higher amount of light scattering than usual.
This needs to be investigated with the film provider.


Copyright images and processing Gert Gottschalk.
Copyright Bilder und Verarbeitung Gert Gottschalk.

Email : drgert1@yahoo.com

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