Hi Morton and other star diagonal users,
About the 'flare' problem: as an old lunar occultation observer I found the same problem with other scopes where a star diagonal is used. The flares may not be caused by your main SCT optics; your C6 may be better than you think. Note that if an object is just outside the field of view of an eyepiece, it can still be within the field of view of the telescope. Then consider the light path through the diagonal.
By viewing the optics - with the eyepiece removed - I found that in many cases the 'flares' were reflections off the tube and sides of the diagonal. Solved this by adding a simple baffle just ahead of the diagonal as described in this technical note:
https://tufi2.files.wordpress.com/20...y-baffling.pdf
That example is specifically aimed at occultation observers. Of course most observers do not need such a severe restriction but the same principle applies. Do some light tracing and experiment with different baffle apertures.
Hope this helps, Alfred