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Zygo Report - Info Please

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The Strehl is the best "bottom line" number in that report if you don't want to get too into what all the different numbers mean, the closer to 1 the better. I think higher astmag numbers and coma (ie poorer) can still give good a Strehl ratio in a poor mirror but both those numbers are low in your report.

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The "Zygo" test results that came with my Orion Optics 8" Europa (De-Lux) Newtonian (and the comparison Zygo test which Orion Kindly did on my Skwatcher 200mm Newtonian), provoked (if that's the right word!) a huge response from many members on SGL here.

The "gist" of which, was that there were so many factors which could influence the actual performance of even the best (most accurately figured) of mirrors, that the "strehl" number would not necessarily give an accurate indication of how good your scope might perform - even if your main mirror was perfect!

As far as I can remember, it all boiled down to "if the views look good to the MK1 eyeball, then the scope must be a good one." Perhaps that's why I found that the views through my f5 Skywatcher 203mm (yes the mirror on the Skywatcher 200, is 3mm bigger), almost matched those of the Orion Optics "8 f4.5 Newt.

But, I would think that knowing that you have an excellently figured Main mirror is a comforting start to good viewing.



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