RoniSimo - Ronchi Simulator

There are several ways to obtain accurate profiles of optical quality surfaces. One is to use interferometric techniques to obtain a high precision measurement, and another is the Ronchi test principle, based on the interaction of several wavefronts reflected from the surface, capable of resolution better than 1µ. The only constraint for surface inspection is that the object surface has to be reflective and opaque. The Ronchi test principle is not only inexpensive, but also provides a dynamic range of measurement in ray slopes which cannot be achieved by interferometric profilers. A potential application of this technique can be the sphericity measurement of a ball bearing.

Ronchi test is an interesting test for the surface of a mirror. For spherical surfaces tested at the radius of curvature of the surface, the test produces straight lines which can easily be measured with the appropriate measurement tools to find out how straight the surface is. The test produces results that show that things are right or not right. Unfortunately, it takes a bit of math to figure out what the actual results are in a quantitative way. However, the qualitative results do indicate whether or not the surface's shape is good or not. Things like zonal errors, especially the turned edge are quite visible in the images.

The general rule of Ronchi testing is that the bands in the Ronchi pattern for any zone become closer together as the grating moves farther away from that zone's center of curvature. Conversely, the bands in the Ronchi pattern become farther apart as the grating moves closer toward the zone's center of curvature.

Today, great help for the amateur astronomers and telescope makers, are the computer, especially simulation programs, that allows us to generate quickly different Ronchigrams and compare they with really observed mirror surface.

Such simulation program is RoniSimo (Ronchi Simulator), that I designed and programmed for the ATMLJ reader. RoniSimo is small but powerful program, that come with nice Gnome Gray interface. It was designed, using the recent programming techniques and trends in the Information Technologies (IT). In the program are implemented a lot of powerful features.

RoniSimo has a single window, that consists a page control wit three tab sheets (Settings, Ronchigram and About). In the first tab sheet called Settings are located all options needed for the ronchigram’s simulation. Additional the settings site is divided in three areas (Ronchi, Grid and Animation), a panels that can be push or popup. By start default popup status has only the first panel, i.e. the Ronchi options, where is the most important data entering. The other two panels can be pushed by the user, and changed the grid or animation options.

Bottom of the window are located two buttons, that perform simulation and animation. By clicking the focus will be automatically changed on the second tab sheet – Ronchigrams (the plot area).

The settings tab sheet includes fields for the mirror specifications – diameter, focal length and central obstruction. The last can be specified in both millimeters and percent.

For computer with different performance, is possible to choose between low, middle and high ray density (number of rays to be traced). Default value is the low selection. Additional the user can choose single or though focus Ronchigrams. Supported are five different light source palettes (red, green, blue, gray and true). The light source can be fixed or moving.

The Grid setup has only four options, that specifies grid density (lines per millimeters), grid orientation (horizontal or vertical), grid defocus (location relative observing plane) and
maximal defocus (+/-) for the though focus simulation.

Finally the Animation setup has options for defocus step (the grid moving amount through the animation), plot interval in ms. The animation can be displayed on the screen only, without saving or saving as animated gif or file sequences (jpg). For the last two options a file name is needed.

From the Ronchigrams tab sheet by mouse right button click appear popup menu with some tools, like printing (includes print preview), saving the graphic in different graphical formats (bmp, gif, jpg, wmf, tiff and pdf) or copy to clipboard. Also by dragging the Ronchigrams can be dropped to other applications that supports OLE automation, for example MS-Word, MS-Excel etc. The same features are available from Ronisimo main menu – Tools.

The Ronchi Test is perhaps one of the easiest optical tests to learn and use and RoniSimo will made it much easier. It is the right tools for the amateur astronomers and telescope makers.

Added:  Tuesday, August 30, 2005
Reviewer:  Ivan Krastev
Score:
Related Link:  http://members.kabsi.at/i.krastev/atm/atmletters.h
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