James Paulson's roll off roof observatory at the Sunridge Observatory site, taken in the summer of 1986, housing a 10 inch f/5 Cave Astrola Newtonian reflector telescope

Sunday, November 20, 2011

Dealing with Dew Issues

One of the problems that amateur astronomers in humid climates needs to combat is the problem of dewing. Dew will form on a corrector plate, eyepiece, lens or secondary anytime they are exposed to the atmosphere and cool faster that the surrounding air. This is especially compounded if the relative humidity is high. The dew point is classified as the temperature at which the relative humidity is equal to 100%

Fortunately there are solutions. Today’s amateur can choose from a variety of electronic controllers and resistive-heating dew straps to wrap around their optics and drive the temperature above that of the surrounding air and keep their optical elements clear.

I recently took the plunge and purchased the Dewbuster controller. The Dewbuster is a premium controller in that it uses a temperature probe to sense the ambient air temperature as well as the dew strip temperature and allows the observer to make a precise setting so as not to create secondary seeing issues caused by applying too much heat. This controller is noted also for its lower power consumption, which may be an issue to consider during long imaging sessions.

To supplement the Dewbuster, I have also purchased the Dew Not dew strips from Agena Astro. These affordable strips are Kendrick compatible and are known for their lower than average power requirements.

This combination will allow me considerable more time under the stars in Spring and Summer when dew is a real issue in my climate. There have been many nights where I have cut short because of moisture issues, and this will help alleviate it completely.