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Dew Shields and Dew Heaters


Dew Shields and Dew Heaters
Dew shields and dew heater systems are an essential telescope accessory for anyone operating a telescope where dew or frost regularly forms. Dew forms on a surface when its temperature falls beneath the dew point. This is a nightly occurrence from spring through fall for those of us in the northeast, your conditions may vary. Dew gives way to frost if the dew point falls below freezing. The formation of dew or frost on telescope optics can render them useless for the remainder of the night. Schmidt-Cassegrain telescopes are notorious for dew formation because of the large unprotected corrector plate at the front of the telescope. The best solution for dew on the optics is to stop it from forming in the first place.

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

Astrozap Telrad Dew Heater
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$35.00
Astrozap Dew Controller
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$105.00
Thousand Oaks Digital Dew Heater Controller
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$105.00
Astrozap Dew Heater Bands
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$25.00
Thousand Oaks Dew Heater Bands
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$39.00
Astrozap Flexible Dew Shield for ETX 90 / C90
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$24.95
Astrozap Flexible Dew Shield for NexStar 4SE
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$24.95
Astrozap Flexible Dew Shield for NexStar 5SE
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$32.00
Astrozap Flexible Dew Shield for ETX 125 / C5
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$29.00
Astrozap Flexi-Heat Dew Shield for Nestar 5 SE
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$64.00
Astrozap Flexible Dew Shield for NexStar 6SE
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$32.00
Astrozap Flexi-Heat Dew Shield for NexStar 6 SE
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$75.00
Astrozap Flexible Dew Shield for Meade LS 6 / LT6
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$34.00
Astrozap Flexible Dew Shield for 8-inch SCT
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$34.50
Astrozap Flexible Dew Shield for 8-inch SCT Notched for Dovetail
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$39.00
Astrozap Flexible Dew Shield for NexStar 8 SE
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$36.00
Astrozap Flexi-Heat Dew Shield for 7' Maksutov / 8" SCT
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$74.00
Astrozap Flexi-Heat Dew Shield for NexStar 8 SE
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$74.00
Astrozap Flexi-Heat Dew Shield for 8" Celestron - 1 Notch
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$82.00
Astrozap Flexi-Heat Dew Shield for 8" Celestron - 2 Notches
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$92.00
Astrozap Flexible Dew Shield for Meade LS 8 / LT 8
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$39.50
Astrozap Flexible Dew Shield for 9.25-inch SCT
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$39.00
Astrozap Flexible Dew Shield for 9.25-inch Evolution
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$41.00
Astrozap Flexible Dew Shield for 9.25-inch SCT Notched for Dovetail
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$41.00
Astrozap Flexi-Heat Dew Shield for 9.25" SCT
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$86.00
Astrozap Flexi-Heat Dew Shield for 9.25" SCT Notched for Dovetail
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$86.00
Astrozap Flexi-Heat Dew Shield for 9.25" Celestron - 2 Notches
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$96.00
Astrozap Flexible Dew Shield for 10-inch SCT
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$47.00
Astrozap Flexi-Heat Dew Shield for 10" SCT
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$93.00
Astrozap Flexible Dew Shield for 11-inch SCT
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$47.00
Astrozap Flexible Dew Shield for 11-inch SCT Notched for Dovetail
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$62.00
Astrozap Flexi-Heat Dew Shield for 11" SCT
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$125.00
Astrozap Flexi-Heat Dew Shield for 11" SCT Notched for Dovetail
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$120.00
Astrozap Flexi-Heat Dew Shield for 11" Celestron - 2 Notches
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$135.00
Astrozap Flexible Dew Shield for 12-inch SCT
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$64.00
Astrozap Flexi-Heat Dew Shield for 12" SCT
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$135.00
Astrozap Flexible Dew Shield for 14-inch SCT
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$88.00
Astrozap Flexi-Heat Dew Shield for 14" SCT
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$155.00
Astrozap Flexi-Heat Dew Shield for 14" SCT Notched for Dovetail
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$155.00
Astrozap Flexible Dew Shield for 16-inch SCT
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$92.00
Thousand Oaks 20" Dew Heater Band HB-20
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$49.00

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.