Protection from dew – advice, please

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    Rene Gedaly

    I had my first experience with serious dew last night during a Messier Marathon and would like to know how to handle this. Looking for low-tech options; I’m practically a Luddite now after a horrible experience with a flip-the-switch, go-to scope that went nowhere. So, I guess I’m looking for basic dew shields and blow dryers? Do they work? Were the electric gadgets invented for convenience or do they actually work better? My main scope is a 10″ Zhumell Dobsonian; will also need something for the aforementioned 8″ GoTo SCT. THANKS.


    Hi Rene,
    We usaly done have a dew problem there only once in a while after a rain. The blow dryers work but you keep having to turn them off and on. I use a kendrick dew remover but any brand should work, I have had mine for 10 years and works great. I think scope stuff has some reasonable ones. See you there.
    Clear skies


    Ray and Rene,
    Here is my experience with dobs, SCTs, TSP, and dew.
    1. Dew can be an issue at TSP. Some years it’s not, but some years it has been for me.
    2. The first countermeasure I recommend is anti-dew wraps for eyepieces. For me eyepieces are the first to fog up. The Kendrick system has worked well for me. I have the basic controller, no need for thermostats I just crank mine to max all the time. I also make a point to keep my eyepieces under a cover at all times. Also make a habit of always pointing the eyepiece in the scope down or at least below vertical when taking a break. Dew forms on surfaces that are exposed to the sky.

    For Kendrick system, give some thought to how you will route the cables so you aren’t all tangled up in the dark. I use velcro wire wrap strips, clothespins, tape, anything that works for the specific situation.
    3. For SCT, you need a dew shield. Mine is a piece of cardboard I rolled up in a hurry one night and duct-taped together and it still works after 20 years. I made it so it slides tightly over the tube.
    4. For Dob, I suggest enclosing the truss system. Not sure what a Zhumell looks like. I have a heater on my secondary mirror. If your dob primary fogs up, the conditions are probably so bad it’s not worth continuing.
    I use a Telrad on my Dob, and have a big cardboard dew shield on it, just used an old box. Again it was taped together casually and has lasted for years. Sometimes the telrad dews up but it’s not a big issue even if it does.

    5. For power source I use one of those car jumper units with a 17ah battery and cigarette lighter socket. Mine does not have a built in light, but if it did I would remove the bulb to eliminate any possibility of an ‘accident.’
    6. Those little 12V hair dryers work ok in a pinch, nice to have available.
    There’s my $.02.

    Rene Gedaly

    Thank you, Sonya. Thank you, Kurt. I believe I can order a solution in time for TSP, and I can definitely get the cardboard, duct tape, and dryer. In fact, I may use the cardboard idea for my binoculars; my 20 x 80s suffered quite a bit last observing session.

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