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		<link>http://r2.astro-foren.com</link>
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			<title>Alistair Gutcher schreibt:</title>
			<link>http://r2.astro-foren.com#comment-215</link>
			<description><![CDATA[You tested the Primary mirror of this Mewlon 180 at it's Radius Of Curvature and it came out as having a Conic Constant of -0.95, (which is a 5 per cent undercorrected Parabola?), even though it's meant to have an Elliptical primary (should be around -0.68 Conic Constant), so you are effectively saying that this Mewlon 180 (older type) that you measured was a Classical Cassegrain not a Dall Kirkham?! Is this correct? Very interesting if this is true. Sorry I am using Google Translate as I don't speak German.]]></description>
			<dc:creator>Alistair Gutcher</dc:creator>
			<pubDate>Tue, 31 Mar 2020 13:41:04 +0200</pubDate>
			<guid>http://r2.astro-foren.com#comment-215</guid>
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			<title>Alistair Gutcher schreibt:</title>
			<link>http://r2.astro-foren.com#comment-214</link>
			<description><![CDATA[Hi, can someone explain to me how you get 0.634 waves of Spherical Aberration from this optic when it tests with a Peak To Valley (PV) on the wavefront of 0.189 (1/5.3) waves?! This seems to be impossible? If I simulate this in Aberrator v2.52, then after I put in the correct numbers for Astigmatism and Coma, I get -0.133 Waves of Spherical Aberration, not 0.634 waves, in order to simulate this optic!]]></description>
			<dc:creator>Alistair Gutcher</dc:creator>
			<pubDate>Tue, 31 Mar 2020 13:23:59 +0200</pubDate>
			<guid>http://r2.astro-foren.com#comment-214</guid>
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			<title>Alistair Gutcher schreibt:</title>
			<link>http://r2.astro-foren.com#comment-44</link>
			<description><![CDATA[2/3 of a wave of Spherical Aberration (SA) is rather disappointing. Admittedly though much of the SA seems to be being generated at near the centre of the optic and so probably has a very minimal effect on the in focus image. At least the optic is smooth and the in focus diffraction image looks good and the Strehl is a good high value. Pity about the diffraction spikes. You would think that for the horrendous cost of this instrument (IMHO) that they could at least give you a clear optical window over the front aperture to remove the spikes on bright stars! Or at least offer it as an option! Regards, Alistair G.]]></description>
			<dc:creator>Alistair Gutcher</dc:creator>
			<pubDate>Sat, 20 Sep 2014 22:24:22 +0200</pubDate>
			<guid>http://r2.astro-foren.com#comment-44</guid>
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			<title>Alistair Gutcher schreibt:</title>
			<link>http://r2.astro-foren.com#comment-43</link>
			<description><![CDATA[Why was the Foucault test and Star Test done on this Mewlon 180 done whilst the primary mirror was still cooling? I can see a rather obvious thermal plume in the image? The mirror's shape is usually different whilst it is cooling, and should not be tested until fully at ambient temperature (i.e. no thermal plume visible at all, at 700x for example, on an artificial star). Was there still a thermal plume when you did the Ronchigram? In which case all of these tests that I mention become null and void, which is a great pity. Was the Ronchigram done in AutoCollimation (where the errors are doubled) or with a point source from far in front of the instrument (no reference flat mirror used) ? I am a little surprised and disappointed at Takahashi's optics (assuming that you tested in Autocollimation for the Interferogram when the primary mirror no longer showed ANY thermal plume AT HIGH MAGNIFICATION e.g. 700x, and also assuming that you are taking into account - in your software - the doubling of the errors through the instrument because of testing in Autocollimation for the Interferogram) since Tak's optics are supposed to be 1/20 lambda PV or better ! "The precision of optical surfaces is at least of λ/20" - see quote here ;- http://www.takahashi-europe.com/en/mewlon.features.php . And these Tak Mewlons are very expensive IMHO.]]></description>
			<dc:creator>Alistair Gutcher</dc:creator>
			<pubDate>Sat, 20 Sep 2014 22:23:58 +0200</pubDate>
			<guid>http://r2.astro-foren.com#comment-43</guid>
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