The best Graduated Neutral Density filters, also called ND grads or GND filters for short, are similar to ND filters, which act a bit like sunglasses for your lens, reducing the intensity of sunlight and enabling longer exposures. However, as the 'graduated' part of their name suggests, ND grads are part dark and part clear, so the darkening effect transitions gradually. They are most commonly used in landscape photography, where the sky is much brighter than the land beneath it, and thus help produce a balanced exposure.
GND filters come in different strengths to help you tame weak or strong sources of light, and also have hard or soft graduations so you can choose one that works best with your transition from light to dark – a dead-straight horizon will likely need a hard graduated filter, while a more ambiguous horizon with rolling hills, buildings, or mountains will need a softer graduation to help transition between your bright sky and dark foreground more gently.
