SVBONY SV172 Lens Warmer, 400mm Lens Heater Warmer Dew, 3 Gear Regulator Temperature USB Universal Dew Heater Strip for Telescope Camera

Be sure to have a good power source.

I bought several of these dew heaters for my telescopes and lens, and found them to be very well made, at a great value.They can be fitted snuggly around the tubes/eyepieces and remain fixed in place. Proper sizing [circumference range] for your intended use is critical, so make sure you purchase the correct size for your application [as they don't stretch (and shouldn't)]As a test, I tried strapping two units in-line to wrap a larger telescope tube and they worked great... just requires 2 USB ports.The included switch/temperature control is compact and very easy to operate. The nice little padded mesh travel/storage bags are a nice benefit too.I was skeptical that these 5v USB powered (vs typical 12v powered units), devices would be able to provide enough 'heat power' to defeat dew onset, but they work very well; and their quick/convenient USB plugs makes hookup (into 60W USB charging hub) quick -n- easy.They need just a bit more time to heat up as compared to older style 12v [higher amps] strip heaters, but they get the job done.Their value to benefit and build quailty is terrific, and I suspect that I should get multiple years use out of them.

These are quite good quality, and seem to work well.Just working on getting a good power supply for the 2 of these (Scope and Finder).Going to use a 12V to USB 6A plug.

Nice kit includes a handy knit storage bag. The 3 level controller can be removed to plug the heater into the USB directly. The 400mm fits my 102mm SvBony perfectly on either the Dew shield or Main tube. Velcro closure is adequate to keep it on, and the overall quality is good.I have used these bands successfully below 20F. Remember 2 amps at 5 volts is only 10 watts at most, and depending on your scope, dew point, etc. results may vary.

It keeps my lens free of moisture. Cable is long enough for some decent cable management. The temperature switch is a nice touch to save power when doing remote astro.