JODAS, © 2001-2006

Testing

Null Test
Simulation
Data Reduction
Millies-Lacroix
Maksutov Mirror Real Profile
Sinnott Mirror Real Profile

See also:
Telescopes

Millies-Lacroix Graphical Approach

Introduction
The method most often used by amateurs telescope makers in visualising the figures of their mirrors is the graphical approach suggested by the french amateur astronomer and telescope maker Adrien Millies-Lacroix (M-L) in the February 1976 issue of Sky & Telescope magazine. This simple method makes interpreting your test data quick, easy, and quite painless. It described a tolerance envelope based on the reflected light rays passing through the theoretical Airy disk. If the zonal measurements fit within the tolerance envelope, then the mirror is judged acceptable. The M-L is a geometric analysis which ignores the diffractive effects of light. A mirror that fails the M-L test can have acceptable Strehl and RMS errors. In addition, since the M-L plot is one of slope and not surface profile, the M-L test cannot, without further processing, tell us if a particular mirror zone is high or low. M-L succeeds by concentrating the telescope maker's attention on zonal measurements. Hitting the zonal measurements as accurately as possible is the best path to a good mirror. However, the slope measurements need to be integrated to obtain the true surface profile across that mirror diameter.

Input Data
On the applet front panel you can change three mirror parameters: clear aperture, focal length and squared eccentricity. Additional settings are available by pressing the Settings button (blue collored). It allows you to enter up to three different series (KE measurements) and up to ten mirror’s zones per serie or setup the light source. If you have not nough data leave the fields blank. From the settings panel are available also two other buttons, Example and Clear; the first fill the series with stored in the applet source KE data; the second button clear all series data. The Close button will leave the settings panel and redraw the graphic with the new options.

Standard Plot
The horizontal axis of the graph represents the radius of the mirror from the center (toward the left) to the edge (toward the right). The vertical axis is the deviation knife-edge travel, i.e. the longitudinal aberration LA. The horizontal central line of the graph represents a perfect parabola. The envelope created by the upper and lower lines represents the tolerance of error in knife-edge measurement for the light returning from the mirror to fall within the diameter of the Airy disk. Typically, when the zone plots are measured within this envelope simultaneously, the mirror is diffraction limited.

Parabola-Removed Plot
If a large and deep paraboloid is being plotted, the dS curve and its envelope rise very sharply, making the analysis difficult. An alternative plotting is the Parabola-Removed plot. This plot is created in much the same way, but before values are plotted on the graph, the values for the perfect parabola are subtracted (for both upper and lower tolerances and the real KE data). The ideal mirror curve in this case is represent by the x-axis itself. We can add or subtract a constant value to all our zonal readings (an offset) to shift the lines up or down on the graph. Doing so has no relevance to our mirror's figure. Essentially, we are adjusting the plot in the same way that re-focusing we are adjusting the plot in the same way that re-focusing adjusts the intercepted cone of light from your finished mirror.

All calculations are based on the Knife Edge measurments. Such data for demonstartion can be loaded in the applet setting arrea, by pressing the "Example" button.

Bellow is listed the applet tag, that allows you to customize it by start, including initialising of the mirror parameters (diameter, focal length, squared eccentricity), light source type and wavelength; auto or user defined scaling; setup series and scale color, plot window background and applet title.

Applet Tag: Note: Relation between index number and color:
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