You can leave this UV filter on your lens at all times to protect from minor bumps and scratches. It also absorbs UV light, which can result in outdoor photos that appear hazy.
A high-perfomance filter for digital cameras
Hoya's Pro 1 series of filters are specifically designed to improve the optical performance of your digital camera. A special multi-coating reduces the appearance of lens flare and ghosting. The filter's low-profile black almite frame and black-rimmed glass minimize reflections.