What are they? A ﬁlter is a piece of glass or resin that is placed in front of your lens to modify the light entering the camera. They’re either circular or rectangular in shape. Circular ﬁlters screw into the ﬁlter thread on the front of the lens, and square ﬁlters require a ﬁlter holder to keep them in place. The most common varieties are ultraviolet (UV), polarizers, and neutral density (ND) ﬁlters.
Who are they for? While polarizing and neutral density ﬁlters are more popular with landscape and architectural photographers, UV ﬁlters are intended for all photographers, from enthusiasts to professionals. Traditionally they were designed to reduce the negative impact of UV light, but today’s sensors aren’t adversely affected so they are essentially redundant on the optical side. Instead, they act as protection for your lens’ front element, reducing t risk of dust and scratches that would otherwise damage an expensive bit of kit.
What are the benefits? Aside from providing a protective barrier between your lens and the environment, ﬁlters can modify the light entering your lens to create different effects which are not achievable in post-processing. Polarizing ﬁlters reduce the amount of reﬂected l reaching your sensor, and are great for making blue skies more intense, vegetation appear more lush, and minimizing reﬂections from water or glass. Neutral density ﬁlters act like a pair of sunglasses by reducing the amount of light entering your lens. This allows the use of longer shutter speeds or wider apertures in brighter conditions.
What are the downsides? By introducing an extra piece of glass into the light path, you will slightly decrease image quality and increase the chance of ﬂare or ghosting occurring. Polarizing ﬁlters will reduce the amount of light reaching your sensor by 2-3 stops, so will dramatically slow down your shutter speed. Higher quality ND ﬁlters aren’t cheap; they can cost over $100 and despite being called ‘neutral’, they can still produce an unwanted color cast.