John,
I clearly am missing the point, as it seems like you are having an each way bet here.
The fact there is variation comes as no surprise, but a skilled practitioner will know from one of his measurements what to trust and in what circumstances.
I would not trust an optic that was only subject to one test. The opticians who I deal with make as many tests as possible....which is a very different regime to mass produced optics which I have seen first hand to be a cursory inspection at best.
I suspect therein lies the rub: testing=time=money.
Skilled observers *can* see the difference between average and excellent optics, and simply saying an optic is "diffraction limited" or 1/4 wave will shed no light on whether an optic is excellent or not.
When Jones, Ceravolo Christen et al. tell me an optic has a Strehl of 0.96, while you may not accept it, I tend to believe them.
Plus it beats flying to Chicago or Atlanta to perform a star test on the instrument before they ship it out
Quote:
Originally Posted by ausastronomer
I am saying the numbers are a lot less relevant and meaningful than many people perceive.........
.........they demonstrated things perfectly. All the mirrors were made and tested by the same skilled person (Ceravolo) on the exact same equipment, using the same methods and conditions. This is the exact point I am trying to make and that Aster, Mark and others also referred to, and you are missing.
Cheers,
John B
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