Thanks for the replies.
Barry your reply got me thinking. When I observe i turn my head slightly to the left (I use my right eye) I think so I have my nose well away from the eyepiece, so I am looking through a thicker part of my glasses. That may be contributing to the diffraction effect.
I also reflected that the effect was most noticeable with brighter stars. implying that the 20" makes this even more noticeable.
Niko
I'll gift you a look through it at SV in March!
BTW I have sent a PM
Malcolm