Hi Markus,
Have a read through the article I wrote on Newtonian cooling. It also goes over dew control as the two are closely related. I covers the use of fans and heaters, their best practice & incorrect applications:
http://www.iceinspace.com.au/63-771-0-0-1-0.html
I don't always look to control dew formation on my optics. Many times I let things just happen, and just call it quits like Bill does - it also means everything is also getting wet, soaked and uncomfortable. Other times, for increased productivity, yes I implement some dew control measures.
Alex.