Quote:
Originally Posted by Satchmo
You would need to qualify that: were they mirrors in the larger ultra fast sizes like F3.7 ? And who did the tests - was it with a foucault test ? Or Null interferometer . I would go further and say that an true 0.8 Strehl mirror free of significant figure distortion problems in a large fast size would be a great performer . Unfortunately I've found a number of epic fails in 20" + sub F4 size amongst a number of USA makers - I would be very surprised if a Chinese company were doing a lot better for half the price !
The fact is that large sub F4 mirrors are much harder to make well - polishing and testing techniques that work easily for smaller slower mirrors can start to fail when applied to larger mirrors - no matter how great your enthusiasm might be .
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I think the mirror tested was 16" f4.5? I believe it was fully bench tested. I can't remember all the details but the paper work that came with the mirror had a very high strehl. Like in the high nineties. The owner didn't believe it and he was right. Apparently the paperwork that came with the mirror only tested one axis of the mirror - whatever that means. I don't know the full details of how its done - I imagine you do. But, the results were inflated. It still turned out to be a great mirror. The owner didn't want or thought it needed to be re-figured.
Who knows what the quality of their sub-4 mirrors are like? For the price I would settle for diffraction limited. I mean, if the one I get isn't to my liking. I can always send it to you for a re-figure, right? Right?
