DewBuster™ Controller Frequently Asked Questions

Newtonian Telescope Questions

I have a Schmidt-Newtonian, should I use the standard sensor or the special Newtonian sensor?
Schmidt-Newtonian telescopes have corrector plates and use heater strips just like Schmidt-Cassegrains so the standard sensor should be used. Follow the same guidelines as for Schmidt-Cassegrains.

Can a DewBuster™ controller be used on a Newtonian telescope?
Newtonian primary mirrors are a relatively thick piece of glass which means they retain heat and thus seldom dew up. Most large Dob's use cooling fans that blow air on the back of the primary mirror to help it cool down to the air temperature. A shroud is very important because it acts as an extremely long dew shield. This helps keep the primary mirror from dewing up after it cools to the air temperature.

The secondary mirror will often dew up because it is closer to the open end of the tube so the shroud is not an effective dew shield for it. The secondary mirror is also a much thinner glass and mounted in an aluminum housing which dissipates heat. I usually recommend the  AstroSystems Dew Guard as a nice compact solution, but the DewBuster™ controller can be used.

The DewBuster™ controller can also be used without a temperature sensor in "Manual" mode to warm the eyepiece, finderscope, Telrad, and other auxiliary optics but not the primary mirror. It will still utilize the Low Battery circuitry to prevent running your battery too low and damaging it.

On large Newtonians the DewBuster™ controller can be used to control a heater attached to the back side of the secondary mirror by using a Newtonian Temperature Sensor with the DewBuster™ controller. The Newtonian Temperature Sensor may be purchased alone or substituted for the standard sensor when ordering a DewBuster™ controller.

Why does my primary mirror stay dew free all night yet it dews up in the morning ?
Large Dobs may experience condensation when the morning sun warms the air and moisture condenses onto the primary mirror because it is still cold from the night air. The most efficient way to prevent this is with air tight covers over the primary mirror so that the morning air can not come in contact with the cold mirror. If the covers can not be made air tight, a heater on the primary mirror can help and it can be controlled by the DewBuster™ controller by using a Newtonian Temperature Sensor.  The primary mirror heater and temperature sensor are left unplugged while the telescope is in use, but when the telescope is covered for the night they are plugged into the DewBuster™ controller so that when the sun comes up the heater will keep the mirror above the air temperature and prevent morning condensation. The mirror should still be sealed from the morning air as much as possible to reduce the heat energy needed from the heaters.