- Effective 20 mm heating length to prevent fogging and condensation on lenses and telescopes in cold weather photography. Fits lenses or telescopes up to 150 mm in diameter and 475 mm in circumference (approx 18.7 inches). - USB powered: compatible with USB 5V 2A sources. Includes a 4.9 ft / 1.5 m cable for flexible use indoors and outdoors. - Versatile use: not only for lenses and telescopes. A multi purpose heater that can keep a mug warm or provide warmth to the wrist, elbow or ankle when cold. - Ideal for photography enthusiasts: a reliable solution to prevent fogged optics during cold weather shoots, helping maintain image clarity and shooting continuity. Use scenarios: - Outdoor winter photography with telephoto lenses; connect to a power bank or USB charger to keep optics clear of condensation during shoots. - Astronomy or telescope setups on chilly nights; helps maintain clear optics for longer observing sessions. - Break time warmth at field shoots: place under a mug or use to warm small body areas during cold working conditions.