Telescope Dew Solutions

Imagine you’re setting up for your first clear night in weeks. You have your camera connected, battery charged, perfect polar alignment, and everything is going swimmingly. After an hour of imaging, you might notice your views through your telescope eyepiece or camera start getting faint and dim. You check the front end of your telescope and it’s completely covered in dew! If you’ve done amateur astronomy long enough, you’ll know how frustrating this can be if you don’t know how to properly combat dew buildup. In this article, we’ll be talking about the best ways to ensure your telescope remains dew-free for your observing or astrophotography session.

Recognizing When Dew Will Form

First, it’s important to know exactly when dew will form. If you live near a large body of water or in a humid climate, dew formation will plague you for many nights. Dew forms as the temperature outside reaches the dew point - or the temperature where water droplets condense enough to where dew begins to gather. If your telescope is at the same temperature as the dew point, moisture will begin to condense on your optics. Dew is very common in the summer when it’s humid outside, the dew point is high, and there’s little-to-no wind. Likewise, in the winter frost or even ice can form anytime the exterior temperature drops below 32 degrees.

Celestron Dew Heater & Power Controller

Looking for the ultimate way to keep dew off your telescope mirror? Celestron has released their Power Controller that enables you to power up to two dew heaters at once. The Power Controller comes with nine ports, two for your dew heaters, two 12v output ports, two aux ports, and a PC port to monitor the status of your dew controller via a program like CPWI. Additionally, if you have an 8-14” Schmidt-Cassegrain or RASA, you should check out the Celestron Dew Heater Rings. These dew heater rings can be installed directly in front of your optical train. The controller uses the ring's built-in thermistor and its internal environmental sensor to provide just the right amount of heat to the corrector to prevent dew based upon the ambient temperature, ambient humidity, and temperature of the Schmidt corrector, which can dramatically reduce the ring’s power draw, greatly increasing battery life.

Preventing Dew Buildup

1. Dew Shield

A dew shield is a quick, easy, and affordable way to lengthen the amount of time you can spend outdoors. While it doesn’t 100% prevent dew buildup the entire night, a dew shield will prevent dew from immediately forming on your front-end lens or corrector plate. The dew shield will also help insulate your telescope, keeping it warmer and the temperature of your optics just above ambient temperature. The dew shield also has the added benefit of helping to prevent stray light from entering your optical path. If you live in a climate where dew is not common, then a dew shield might be all you ever need.

Apertura Dew Shield

2. Keeping your telescope in a warm room before bringing it outdoors

Another useful tip for helping to avoid immediate dew buildup is to keep your telescope stored in a warm, dry room. Recall how we mentioned that dew will form when your telescope’s optics reaches the same temperature as the dew point. You can lengthen the amount of time it takes for your telescope to reach this temperature by keeping the optics warm before taking it outside.

3. Dew heaters

A dew heater is by far the single best method to prevent dew from building on your telescope’s optics. A dew heater works by placing a heated strip around the parameter of your telescope. This ensures that the telescope optics stay above the dew point for the entire duration of your night. The downside to this is that a dew heater requires some sort of power hub to be able to run properly.

4. Using a fan or a hairdryer

Another method to slow the formation of dew is to keep some sort of airflow going around your telescope. This can be done by using a medium-sized fan. Another added benefit to this is that a small fan can help blow pesky mosquitoes and other bugs away and add to your overall comfort! Additionally, many astronomers also use hairdryers on a low heat setting and warm up their telescope’s optics every hour or so. However, you may not find this the most efficient method as the dew will eventually return without a consistent source of heat on your optics. You also might find that using a hairdryer outdoors at 3 AM might raise the ire of your neighbors!

Questions? Contact Us!

Still struggling to combat dew on your telescope? Send a message to our non-commissioned product advisors, our team of telescope experts are happy to help!