Steve,
Diffraction rings outside of focus are extra blurred by atmosphere. It sounds like you have got a decent lens. You should not expect from an achromat a text-book-star-test-for-a-Newtonian a la Suiter. You should only star test to discover collimation problems like coma.
Pay attention to images of the planets and the Moon in focus, try splitting some tight doubles - that's what matters.
Dmitri
Diffraction rings outside of focus are extra blurred by atmosphere. It sounds like you have got a decent lens. You should not expect from an achromat a text-book-star-test-for-a-Newtonian a la Suiter. You should only star test to discover collimation problems like coma.
Pay attention to images of the planets and the Moon in focus, try splitting some tight doubles - that's what matters.
Dmitri
