Quote:
Originally Posted by Peter Ward
I have in my possession a lovely hand-written letter from Roland Christen regarding optical testing and quality.
AP typically deliver PV 1/10th to 1/16th wave optics. Most of this comes from a slight lack of homogeneity in the glass itself. Their Strehl cut-off of 98.4% or better....however...Strehl can be a little useless without enough data points.
AP use a super-smooth polishing technique to get the RMS figure down to 1/50th of a wave (or better!) , plus sample hundreds of data points in 5-8 orientations to produce a Strehl number they can rely upon.
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sigh...Obvious marketing jargon from AP - people love the term "super smooth polishing", look at zambuto for example. Once the pitch lap is on and conformed, there is no such thing as "super smooth polishing"
It comes down to technique.
I highly doubt AP stops figuring because of errors in the glass - It is more likely that they recognize that no one will notice or care that the optic is better than 1/10 wave. But to let an optic slip that badly as the wavefront shows... I'm confused. A massive TDE like that is a rookie mistake - if that wasn't there, sure the lens would be great, but that is sure to produce a visible issue at higher powers. As the scope is used for imaging though, it will do the job nicely.
That's just my (most likely controversial) opinion, from someone tho has made a few optics and used an interferometer.