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Optical quality ratings are so universally abused by opticians as to render them essentially meaningless unless derived from a test done by an independent 3rd party. Some questions to ask are; Was the test done using the full aperture (was the edge masked?)
Was the astigmatism term deleted? (a common practice believe it or not)
If the optic is a refractor... what is the performance of the objective from c - f
Was the strehl derived from an actual measure of the whole optic or an inferred figure of revolution derived from measurements taken over a small percentage of its surface.
Was the test structured to report the level of correction for a source at infinity... or have they conveniently removed the Z term and blown smoke over it under the guise of propriety 'testing technique' as one well known British manufacturer is known to do.
You get the gist I hope.....
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