^^ at F/5, coma does become a problem. For example, using my TV 32mm plossl in my scope is like looking out the window of the "Enterprise" at warp speed
You can always buy high end eyepieces, such as Naglars, Panoptics and Vixen LVws which have better edge correction. My Vixen LVWs have noticably better images than my plossls in my 10" F/5.
Those "ripples" you descibe in your 5" are probably baffles inside the tube to combat stray light. Maybe post a pic so we can be certain?