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Sounds like a question for Bird.
I'm not sure myself what "strehl" actually means though I'm familiar with the fraction of wave rating for most optics. I have a Takahashi Dall Kirkham with mirrors figured to 1/20th of a wave. It's great at high power on planets. That said, my understanding is that once you get much better than say 1/4 wave optics the returns in terms of improved images diminish rapidly. For low power work I'd be surprised it there is big gains to be made from figure accuracies much beyond this.
cheers,
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