Question: I’m not sure which neutral density grad filter to buy. In what way are hard and soft grads different?
Answer: If you’ve ever shot around sunrise or sunset, you’ve probably noticed how difficult it can be to get the land and the sky exposed correctly in a single shot. This is because the range of light intensity is unusually large, and may even be outside of the camera’s dynamic range. Some parts of the image are simply recorded as pure black or pure white, devoid of any image information. To get around this problem, an ND grad can reduce the light intensity in the sky. ND grads are single sheets of glass or plastic that are tinted at one end, gradually changing to clear at the other end.
This effectively reduces the light intensity range in the scene. It’s the same principle as the tinted strip that you often get at the top of a car windscreen. ND grads are most frequently used by landscape photographers to control bright skies, allowing them to expose the sky and the land correctly within the same image. There are ND grads to suit different shooting situations, so before you invest, think about which you’d get most benefit from.
The first thing to consider is whether to buy a hard or a soft grad. This refers to how steep the gradient is between the tinted and non-tinted parts of the filter. In other words, how rapidly the tinted glass becomes clear. If you’re shooting landscapes with a very flat horizon, such as coastal scenes, a hard grad, where the gradient is very small, is ideal. On the other hand if you shoot mountain environments, where the horizon is not so flat, the wider gradient of a soft grad is better.
Choose the right strength
The second thing to consider is the density or ‘strength’ of the tint. Darker densities tend to suit sunrises and sunsets, whereas lighter densities tend to suit daytime conditions. If in doubt, invest in a grad kit with a range of densities and hardnesses. Cokin’s H250A ND grad kit is a good option, although as a P-size kit it won’t suit ultra-wide focal lengths.