UV filters are most commonly used to protect the front of your lens. A first line of defense against scratches, rain, dirt and dust. Hoya NXT Plus UV is a powerful upgrade to the NXT series. The new filter applies a waterproof top coat to smooth polished Schott B270 glass for easy cleaning. Dirt, stains and water wipe away easily. Using 10 layers of Hoya's proprietary anti-reflective (AR) multi-coatings, your images display better contrast, color and sharpness with 98% light transmission. Therefore, leaving it on all the time will not damage your images. NXT Plus filter frames are precision milled from lightweight aluminum for a slim profile making it perfect for all lenses, including super wide angle. The frame has full front filter threads that can accept a regular lens cap or allow you to stack additional filters like a circular polarizer or neutral density. What else does a UV filter do? Most photographers leave a UV filter attached to the lens at all times as a form of protection. But the filter also plays an important role in filtering through UV Haze. It's not a big deal when you're taking photos at sea level, but as you hike to higher altitudes, the filter definitely helps cut through the haze to increase contrast and improve color. The NXT plus has a UV cutoff point of 360nm or L36 which is higher than most filters at this price.