Quote:
Originally Posted by Stefan Buda
Damn good this test. Clearly shows the low zone near the edge of the primary, that I knew about (not significant), and the slightly turned up edge.
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Yup, it also easily picked up the "by design" residual high order spherical at mere 13nm! (undercorrected primary plus two lens corrector leave some minor residual aberrations uncorrected - this is unavoidable consequence of all CDK's).
It always surprises me to see that people still go to inordinary lengths using all sorts of lyrical adjectives and convoluted descriptions to describe how good or how poor their optics are. Roddier spits out all the gory details, in
numbers, not bullspeak. And it takes just about the same time to perform as a decent (eyepiece) star test would.
Yes, it does take a bit of a learning curve as well as decent preparation, but it still amazes me to see this test not being more widely embraced by amateurs.
Perhaps it leaves too little to wax lyrical (well, none) - it sounds much more boring to talk about secondary quadfoil in nanometers rather than of "diamond specks of dust on a black velvet" and "needle pinpricks of light".
Oh well.