ND grads Fade to grey
A graduated ND filter is dark at the top graduating to clear at the bottom. They’re used to ‘balance’ scenes that have a dark foreground and bright sky. They come in ‘hard’ and ‘soft’ types, referring to the severity of the transition between clear and dark. Hard grads are great for level horizons, but soft grads are usually the better option as they’re more forgiving in undulating landscapes. To calculate the filter strength you need, expose for the foreground in Manual mode, then take a reading of the sky towards the top of the frame; if it’s showing three stops overexposed then you’ll need a three-stop filter.