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How to Combat Telescope Dew

How to Combat Dew on Your Telescope

It’s a beautiful night - the perfect night for stargazing. Not a single cloud is present to obscure the view, the stars are out in full, and nothing could spoil the incredible sights you’re about to see.

Until a misty haze settles over the star you’re focused on, and dim objects recede into nothingness. What on Earth (or in the cosmos) is happening?

Stargazing presents some unique challenges, not the least of which is finding incredibly small objects in a vast sky and figuring out the right magnification for optimal viewing. The last thing you’d expect to ruin your night is telescope dew, a thin film of condensed water that doesn’t go away no matter how many times you wipe at it. 

Telescope dew is your enemy, and it’s not going to go away without a fight. Luckily, with weapons like telescope dew heaters, dew shields, and dew controllers, you can take up arms against this threat. 

Why Dew Forms on Your Telescope

A few simple factors contribute to the formation of telescope dew. Sadly, many of these factors are beyond your control. Dew is condensed water that used to inhabit the form of vapor when the air outside was warm, but once that air started to cool, the vapor had to change form and go somewhere else — namely, your telescope. The prime time to set up your viewing tools for the night happens to be when the ambient air is cooling off, and bringing your toasty warm telescope into an environment that’s cooler than it is creates the perfect conditions for dew.

How to Fight Back

Though it might be tempting, try to refrain from wiping off your telescope’s optical surface. Not only will it not help, since the surface has already cooled down enough to allow dew to form and it will just keep coming back, it’s also best not to touch the optics at all. If you absolutely have to, you can use a soft cloth, and be sure to dab gently instead of wiping.

Many telescopes have some dew protection, but in many cases it’s just not enough. The only type of telescope that’s generally safe is a Newtonian, because their mirrors are deep within the tube. Everything else will need a little extra help - that’s where telescope accessories come in.

Telescope Dew Shields

One of your basic options is a dew shield, which can delay the formation of dew but will not prevent it entirely. They are essentially hollow shells that extend the tube of your telescope, keeping away the moist air and providing more protection to the optical area. There are a wide variety of shapes, sizes, and materials to choose from when it comes to dew shields. Many are made from flexible, lightweight materials, making them convenient and easily portable accessories to keep on hand.

While dew shields can slow down the cooling process, they don’t stop it - that’s where dew heaters come in.

Telescope Dew Heaters

As we said, dew forms when the air temperature drops, forcing water vapor to condense and settle on any surface it can find. In order to make your telescope an inhospitable environment for dew, you need to keep it just a touch warmer than the air around it. Dew heaters are more than up to the task.

Telescope dew heaters are strips with heating elements inside them that wrap around your telescope and provide a constant source of warmth near your optics, preventing dew from forming on the cooled surface. Keep in mind and plan ahead: the heater needs to be plugged into a controller (to adjust the heat radiating from the dew strip), which needs a DC power supply.

Heated Dew Shields & Controllers

Get the best of both worlds when you combine a dew shield with a dew heater. Essentially a shield with a heating element built in, these offer protection and prevention, giving your optics the best chance of staying clear and ready to reveal the glories of the night sky. You’ll need to couple your heated dew shield with a dew controller, which will allow you to make finer adjustments to compensate for the temperature and weather and keep your telescope only as warm as needed to keep dew from forming.

Hairdryer

The economical route is always an option, but it does come with a few caveats. Many astronomers choose to use a tool they already have at home to banish dew - a hairdryer. If you decide to do the same, make sure you set it to the absolute lowest heat setting, and don’t let the heat linger on the optics for too long. There’s also the chance that your hairdryer will blow dust and other contaminants onto your mirror, which will interfere with the crispness of the image. Use this method with caution.

Win the Fight Against Telescope Dew

Telescope dew doesn’t have to send you packing! With the right tools, you can extend your viewing sessions and enjoy even more incredible sights. Need help selecting the proper dew prevention accessories for your telescope?  Contact our non-commissioned product advisors at 800-266-9590 or info@highpointscientific.com.  All purchases made at High Point Scientific qualify for Free Lifetime Tech Support.  Happy Gazing!