Photographing the ocean is a challenging and rewarding subgenre of landscape photography. The are a myriad of different ways to photograph the ocean with the potential to use many different filter types. Here are my recommendations for seascape shooting regarding each individual type of filter.
Shooting seascapes is often complemented by dramatic lighting conditions with wet reflective surfaces such as rocks. A CPL is useful to reduce the reflections coming from the water itself (allowing see through to a rock pool for instance) and from wet rocks. It can also enhance the textures of a cloudy sky. I would avoid using a CPL where the reflections of colourful light are desirable, or when shooting into a plain blue sky as the CPL can cause banding if used in the wrong orientation.
@ Dylan Toh With NiSi Ti CPL
When shooting at a level horizon into the sun, I would often use a hard edged GND or a reverse edged GND to balance the lighting. When shooting away from the sun, I would typically use a soft or medium edged GND instead. I would avoid using GNDs when there are large objects breaking the horizon line such as sea-stacks, or if shooting dramatic wave action where the waves themselves cross the horizon line.
@ Dylan Toh With NiSi Medium GND 8
I use the strength of ND filter that allows me to achieve the shutter speed that I want. For instance, I may use a 3 stop ND filter to achieve trailing water with a shutter speed of ¼ second. In order to achieve a smoothened water, the minimum strength of ND filter I would use is a 6 stop ND filter for exposures 30 seconds or greater. If it is still before sunset or just after sunrise, you may need to use a 10 stop ND filter in order to achieve this effect.
@ Dylan Toh With NiSi ND 64 + Medium GND 8
How to Get Started with Long Exposure Photography
by Dylan Toh