C087 * Newton-Mirror - two times tested
Siehe auch : C090 * Testing mirrors in two steps
This mirror suffers a car accident - so I've tested it for a second time, in the same matter with two steps I descriped it here:
http://www.cloudynights.com/topic/490641-newton-16-f45-carbon-fiberall/page-2#entry6849699 , 2nd Link, So let me show
this way again and the results of this.
In a first step let us check the astigmatism value just in Radius of Curvature . With this setup you have to respect seeing-, mirror storage-,
the Bath interferometer- and of course the astigmatismus of your testing mirror itself and no additional flat with an autocollimation setup. So
I use the RoC setup for minimizing the effects what causes astigmatism. I'm looking just for the astigmatism value of this Newton mirror itself.
The fringes map shows an insignificant value at the RoC setup.
But let us check the value of the rest astigmatism with AtmosFringe: In RoC and just the astigmatism value.
This shows the wavefront distortion . . .
and a value of PV lambda/9.5 for astigmatism you can neglect this one. It's insignificant and for visual or fotografic use.
Now, let's start with the second step: Setup in autokollimation: With this setup the flat mirror introduce additional astigmatism.
So it's better just calculate the spherical aberration with this setup. The Foucault test shows the surface quality: It seems to be
very smooth, without spherical aberration.
The next Ronchi test shows the spherical aberration better (over- or undercorrection ) and the surface smoothness again. See here again:
The Lyot test is the last one to show the smooth surface of this mirror. (http://www.astrosurf.com/tests/contrast/contrast.htm#haut)
In this autocollimation setup I create several fringes maps and calculate just the spherical aberration - this must be a hight Strehl value, the
fringes map shows it.
So the Spherical is about PV L/11.5 and the astigmatism before was PV L/9.5. More than adequate for visual and fotografic use.
The wavefront diagram shows a slightly overcorrected mirror PV L/11.5 - this is OK.
At last an artificial fringes map that shows a slightly overcorrection.
So this mirror should be sufficient for a serious observer.
You are invited to comment this report.