It reduces the angular amount of sky seen by the telescope objective and can keep moisture at bay for an extended period of time.Īs an added benefit, a dew shield can increase the contrast in your images by acting as a light baffle. (As well as eyepieces, mirrors, etc.) Using a Dew ShieldĪ dew shield can effectively delay the process of dew forming on your optics, but it won’t stop it completely. This chain of events causes condensation to form on your telescope or camera lens. When the telescope radiates its heat to the sky, it quickly cools down and drops below the dew point temperature. To be a little more technical, the heat from the warmer telescope transfers to the colder outside temperature via radiation. On a night with high levels of moisture in the air, dew forms even more aggressively.Ī telescope that has been “dewed-up” no longer captures clear images of your deep-sky target, and instead captures a washed-out featureless image that resembles a flat frame.Īs the ambient temperature drops, condensation can accumulate on your telescope When the surface of your telescope objective or camera lens drops below the ambient temperature of the air outside, moisture begins to condense. Those who shoot with an SCT ( Schmidt Cassegrain Telescope) or Newtonian reflector will need to take extra precautions to keep the optics free of moisture on their larger optical surfaces. Before we look at a few solutions, let’s take a look at what causes dew to form. I shoot primarily with refractor telescopes like the Explore Scientific ED102, which are quite easy to manage due to their small size and retractable dew shields. Ultimately, the method you choose will depend heavily on the type of telescope you are trying to keep dry. These range from dedicated tools designed specifically for moisture prevention, to free methods using everyday household items. If you have ever felt the sting of an imaging or observing session spoiled by dew, the good news is that there are many effective solutions available. Understanding Dew Heaters for Astrophotography Make sure to order a dew heater band with enough length to reach the objective of your telescope from the USB port. They can easily be plugged into your power bar or portable power station with powered USB ports. I personally prefer to use USB-powered dew heater bands whenever possible. If you’re using RCA jack style dew heater bands, this is a great option to consider. The Pocket Powerbox also includes 4 x 12V ports to power other astronomy devices such as your camera, motorized focuser, or even the ZWO ASIair Plus. It is important to make sure that your dew heater band cables will not catch on anything as your telescope tracks the motion of the night sky throughout the night. The most practical aspect of this option is the fact that my cables are managed much more neatly, without fear of a cable snag. In the configuration shown below, you’ll see the dew heater band plugged into the Pegasus Astro Pocket Power Box. I have used many dew heater bands over the years, from simple USB-powered devices to the traditional “RCA-type” bands that require a controller to run. There are a number of solutions available for keeping your telescope objective moisture-free.ĭew heater straps on my main imaging telescope and guide scope Using dew heaters with your astrophotography rig can be the difference between capturing hours’ worth of exposure time on a target, and coming up empty-handed (trust me).ĭew prevention is an essential precaution needed for long exposure imaging sessions and is something you will inevitably need to address at one point or another.
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