Hi....
[Why would someone use a hard graduated ND filter when shooting a sunset sea view !!
I thought ND filter are supposed to be used to block daylight not low light !!
Thanks ....
Below is an example. To capture the colors, or equalize them a bit better, the ND was used up top because the reflection off of the water is not going to match the direct light of the sun over the horizon. The filter allowed me to equalize brightness and capture a near duplicate between the sky and the water.
Sorry for the poor quality of the image. It's from a thumbnail on my phone.
They can also be used when the sky is so overly bright that it would be washed out without a graduated ND filter. It has to do with our eyes being able to see a greater dynamic range than what the sensor can capture. Using a graduated ND filter can bring that dynamic range into something that the sensor can record without blowing out highlights or losing details in the dark areas.