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

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.

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.

Keeps the lens warm like it should

I’m giving this a one star review. While I know it’s a sample of one however, when trying to power it on for the first time the cover caved in jamming the button. After peeling off the plastic cover to unjam the button underneath I was able to get it to power on (at least the indicator light). When it finally did turn on I could not feel if it was actually warming anything and after waiting several minutes I gave up. Again this is my sample of one but I would look for an alternative and not recommend purchasing.