We are having a problem with our scopes on cold nights. (-10F is about average here.) One poorly aimed breath means that the eyepiece lens fogs. We have to remove the lens and keep it under our arms to warm up to clear it.

The scopes are wrapped with heating tapes which does seem to keep the large lens from fogging/steaming up. It is the eyepiece lenses that we are having issues with.

I searched Orion & Celestron's websites, but they just offer heating tapes which we already have. I am concerned that frequently wiping the lens free of moisture, even with a soft cloth, could eventually scratch the lens.

Does anyone have a solution?


1 Answer 1


Dew-heater bands (straps) do come in sizes even down to 1.25" and 2" eyepiece. Multiple vendors make these. Dew-straps are something of a standard in that they are resistive heat-straps designed to run on roughly 12v power. The typically use the (RCA) tuplip type plug. The dew-strap and dew-controller typically do not need to be made by the same vendor to be compatible.

Check vendors such as AstroZap, Dew-Not, Kendrick Astro Products, and others.

Depending on your dew controller, you may need a controller with additional channels. Multi-channel dew-controllers allow you to set different power levels for each channel (or at least for groups) since the amount of power needed to heat, say, the corrector plate on a large telescope is much more than the power needed to heat a tiny 1.25" eyepiece.

If you have adequate power, you can use a hair-dryer to defrost an eyepiece (although I prefer the dew-heater strap to prevent fogging.)

  • $\begingroup$ Found and ordered a larger dew-controller and heat tapes for eyepieces that were not available on either Orion or Celestron's website. Thank you for the tip about other sources. Until they arrive, I like your hair dryer idea. $\endgroup$
    – Bookaholic
    Jan 9, 2021 at 17:33

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