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Advice needed final collimation on a star?
It is often mentioned that final collimation on a star is important in fast newtonians. Some posts on the web suggest looking at the symmetry of the defocussed star image as a guide , however this works fine with SCT 's and maksutovs etc where the secondary is central , but where the secondary is offset as in a fast imaging Newtonian the defocussed image will show asymmetry due to the offset secondary, " not being central"! Looking at the stars "airy disc" requires very still conditions ( I don't think I've ever seen one) , so what are the options besides hoping your mechanical collimation using a Cheshire is sufficient?
Regards philip
PS I've tried laser collimation after using a Cheshire and found no need to touch anything .
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