I have a DSI RC10C (10" RC telescope) mounted on a permanent pier out in the open, no shed nor observatory. I use a Dew strap at the opening and the secondary mirror heater is on. I image with the fans running all the time but even with a slight dew, the primary mirror dews up. Sometimes the dewing is heavy enough to make streaks as the water runs off the mirror! The mirror is 800mm down the tube so I doubt an additional dew shield will have any effect. I have ordered additional dew straps to place on the tube near the mirror but it remains to be seen if that is a good idea, obviously I don't want to affect my imaging.

If anyone has a thought for a possible solution, I would be greatly obliged.
Charles