Quote:
Originally Posted by Gama
You can still get a airy disk and rings on a bad optical system too.
What i would do is see how well it can seperate very close stars and how much detail it can show.
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Thats correct. If for example you see the second diffraction ring from the Airy Disc almost as prominent as the first, under good seeing ,on a 4th or 5 magnitude star , with a medium sized instrument ,that's indicative of 1/2 wave wavefront or more of pure spherical aberration.
Mark