ND grad filters: know your densities
The ND grad shouldn’t be confused with its close cousin, the ND filter. Although they both have similar properties, the light-reducing effect in a graduated filter is only present across its top half, rather than the whole filter.
Also, the graduation can be abrupt (known as a ‘hard step’) or subtle (‘soft step’). Hard-step grads should be used with sharp transitions, such as in seascapes, while soft-step grads are best for more uneven transitions.
Just like ND filters, grads come in different densities, the most common being ND2, ND4 and ND8. Most photographers tend to buy sets of grads so that they can cope with a variety of lighting situations. You can also purchase filter holders to attach the filter to the lens, although they can also be handheld with a little practice.
Like all photographic tools, there are some pitfalls and compromises that you need to consider. Graduated filters are linear, so the effect is uniform across the surface area.
This means that coastal sunsets will suffer from unnaturally darkened cliffs, and city skylines or lone trees will appear as silhouettes, despite looking different to the eye. If you find that the filter usage is noticeable, then you have no choice but to use an alternative strategy in post-processing.
However, in relatively simple scenarios, there’s nothing quicker and more satisfying than using an ND grad to balance the light in a landscape shot. With a bit of practice and some careful positioning, ND grads will give you professional-looking results.