Dew Shields and Dew Heaters
A dew shield is a long extension to your telescope tube, which effectively insulates your front of your telescope. Dew shields work by maintaining a stationary column of air at the front of the telescope, trapping some of the heat within the telescope and slowing the arrival of new moisture, thereby slowing the formation of dew. Over time, the optics will still dip below a dew point, but passive dew shields for telescopes will sometimes work for several hours before dew begins to form on the optics. Typically, telescope dew shields are the less expensive option.
Situations involving longer observing sessions or heavy dew call for active or heated solutions. A dew heater is a specialized strip of resistive electrical wire that fits around the lens of a telescope. The wire is driven with dew heater controller, powered by a 12-volt DC battery, which then runs an electric current through the wire. The high resistance of the wire means it will heat up and directly transfer heat to the telescope, preventing it from dipping below the dew point. Normally a dew heater controller is used to set the desired amount of heat. Adding too much heat can lead to tube currents which will interfere with the image. Though they’re more effective, dew heaters tend to be more expensive. Since they require electricity to work, they also require more power in the field.
Dew Shields and Dew Heaters
Telescope Dew Shields & Telescope Dew Heaters
Anyone starting out in astronomy and observing the stars may notice the occasional formation of dew on the objective lens or corrector plate. This can make for a frustrating observing experience if you live anywhere that dew is common. That’s why dew shields and dew heater systems are an essential telescope accessory for anyone operating a telescope where dew or even frost regularly forms.
Dew and Your View
Dew forms on your telescope when the temperature of your scope’s objective lens or corrector plate falls below the “dew point,” causing moisture in the surrounding air to condense on optical surfaces. This is a nightly occurrence from spring through fall for those living in the northeast, primarily.
Dew gives way to frost if the dew point falls below freezing. You might notice the same situation on a car’s windows in the early morning. However, telescopes are particularly susceptible to condensation because they point directly upward at space, radiating their heat more quickly due to their upturned position. Schmidt-Cassegrain telescopes are especially prone to dew because of the large, unprotected corrector plate at the front of the telescope.
When dew collects on your telescope lens, this essentially halts your viewing experience — the formation of dew or frost on telescope optics can render them useless for the remainder of the night. While you can try to heat your telescope up to get the lens back above the dew point using a hair dryer or other heating device, the best way to handle dew on optics is to prevent it from occurring in the first place. That’s where dew shields and telescope dew heaters come into play.
Get Dew Shields and Heaters
At Skies Unlimited, we offer a wide selection of dew control equipment, including dew , dew heaters and even heated dew shields. We also offer the advice you need to get the most out of your equipment. Since our founding in 2004 by amateur astronomers, we’ve dedicated ourselves to providing expertise to new amateur astronomers, making the field more accessible and easy. Whether you want to purchase a Celestron dew shield or are wondering which telescope dew control measures are right for you, we can help.
Call Skies Unlimited today or visit us at our store located in Pottstown, Pa., to get started shopping with us.