Dew Heaters & Cool-down

This may sound like a stupid question: If the point in cooling down an instrument is equalize the temperature of the objective and tube to the outside temperature, then isn't using a dew heater counterproductive and degrade the image?

Comments?

The job of a dew heater is to prevent fogging of the optic. It only requires a degree or two above the surrounding ambient air. It prolongs natures process. Therefore, it would produce very little if any air currents. Better to be able to see than not see at all. Here in Fresno CA. I live in perpetual high humidity thru-out the winter. Without a heater ALL the optics will instantly fog and I would see nothing !!

I don't know what you'd do with other scopes, but I was concerned about the same thing with my 12.5" Dob. In the past my primary mirror would ocassionally dew up but once I mounted two small fans to blow air over the surface it has never dewed up. This worked so well that I decided to do the same with the secondary mirror. I had a homemade system using resistors but was concerned about the heat. On really bad nights it would still dew up. I mounted another small fan next to the focuser, pointed at the secondary, and haven't had any dew since. To me it's the best solution because it also gets the optics to ambient temperature faster.

Doug Tanaka