I piggy backed an Orion short tube 80 on a 100mm SW refractor which is much longer- no problems as long as the balance and alignment is right and there is no flexure between the 2. Next to it I even had a Meade apo 80mm side by side rig but I think I was overdoing it a bit!
I just found the longer scope a pain to look through in certain directions. Not nearly as neck creakingly bad though as the 10" reflector I have now on the same mount.
Graz
