NEEWER USB Lens Warmer 400mm Lens Heater for DSLR Camera and Telescope

Keep your lens clean from dew, fog, and condensation when spending hours in cold weather to take photographs. Run the heater on a wall plug, portable charger, or other 5V 2A USB power sources 4.9ft/1.5m prolonged cable provides versatility for use under various circumstances. The temperature regulator offers 3 levels (High Mode: 55-65°C; Middle Mode: 45-55°C; Low Mode: 35-45°C) to suit different ambient temperatures.

eBay