Does the infrared camera lens zoom or focus by rotating? It looks like it's doing that towards the end. Something stuck to the front element probably wouldn't

Does the infrared camera lens zoom or focus by rotating? It looks like it's doing that towards the end. Something stuck to the front element probably wouldn't be so much in focus, it should be something deeper in the lens. For example a piece of paint can become dislodged (has happened to me with binoculars).