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Rumples, the scope that showed non-concentric circles was a 10" f/6.3. In spite of this the scope showed pretty good images, but other problems developed in the warranty period and I sent it back. For contrast, a 90's era 8" f/6.3 that I currently have shows nice concentric circles looking into the tube but gives softer images due to higher than average spherical aberration. So I certainly agree with you that misalignment of the optical axis is not desirable, but it may be one of the lesser evils that can afflict schmidt cassegrains.
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