USB Lens Warmer, Lens Dew Heater Strip with Temperature Regulator, Condensation Prevention for Telescopes Camera DSLR Lens Telescope Eyepieces Less Than 3.15 inch (80mm) in Diameter

Astronomy. New to the hobby... and I am so glad these work as well as they do;-) Anyone who stares through a telescope on a winter night would understand. No drama, just plug it in and does the job nicely. Comes with a nice bag (some don't, I have others), has a nice cord that is easy to manage when cold. And the cord has been long enough to work fine for my needs (8"dob with a battery at it's base). I leave it on all night. In the beginning I checked the temperature regularly but now have just settled in to taking it for granted (sigh of relief)

The instruction print is a bit small. To turn on hold the button for about two seconds. What's nice: it's long, and it comes in a nice pouch. Con: It may be just me, but I prefer my cables to be modular, this isn't.

Did the job as described

I use this when doing nightscape photography and it does a great job of keeping the dew from forming on my lens. It has low, medium and high settings and so far I’ve only had to use medium. I power it with a usb battery bank. (Not included) Comes with a pouch that’s perfect for storing hit and the battery together.

I used this USB powered Dew Heater on a 8mm lens for night sky photography, an it kept few from forming on a humid night with temps in the 60s. It heats quickly on the High setting, but Low is recommended for my conditions. I used a 20,000mah portable power supply for over 2 hours continuously without any problems. This power supply has 10W USB-A output, so it has no problem running the heater. I didn't try to measure current, but I did plug it into an old phone charger that has a LED on it, and this heater apparently needed more power than its stated 5v 1000ma (5W) output because the light constantly switching between dim and bright. That tells me that a small, lightweight USB battery probably cannot run this thing, and that may be something you need to consider before heading out for a long photo session.