John,
So are you saying test data provided by (skilled) opticians is some sort of random number that in no way correlates to the quality of the optic?
As I mentioned earlier there are many ways to test optics, and I'd certainly agree some are more subjective than others, but I would not suggest that various quantitative methods are in some way divergent.
An excellent optic makes itself apparent no matter how you look at it.
To paraphrase Ceravolo, interferometry is not necessary to make excellent mirrors, he in fact uses the Foucault test to actually make the optics, but then quantifies the results with interferometry to ensure the optic meets the required performance as it is less subjective than the star test and easily quantified (by him at least)
In fact Ceravolo did a piece for Sky and Telescope (March 92?) where telescopes with mirrors of varying (but known) quality were used side by side to see if anyone could tell the difference visually.
In this case the numbers were not just relevant, they demonstrated perfectly the difference between "bad, fair, good and excellent optics"
Quote:
Originally Posted by ausastronomer
Peter,
I don't agree with this in any way shape or form.
Unless the numbers for each different optic are calculated by the same person using exactly the same test equipment under identical test conditions with identical adjustments and numerical manipulation, the numbers themselves are meaningless. .....
..... The raw numbers IMO are pretty meaningless for comparison purposes, but, if the test methods and conditions are known, they do give you an indication as to the overall quality of the scope. ie. bad, fair, good, excellent.
Cheers,
John B
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