An infra red filter blocks visible light but allows light in the infra red spectrum to reach the camera's sensor. This can create some strange, eerie effects as seen in these examples: trees and foliage reflect more light while water and a clear sky reflect very little and appear darker than usual. Using an infra red filter requires a high ISO and/or a long exposure, typically from 10 to 30 seconds, so there is likely to be some movement blur from the wind or flowing water. Post-processing can help in refining the final form of an image.