There, I’ve said it. It’s probably incredibly unfashionable in this age of digital – in fact I often see people on forums etc discussing selling their grad filters because they have abandoned them in favour of exposure blending – but they are currently my preferred method of attempting to balance exposures.
An ND (Neutral Density) grad (Graduated) filter is basically just a piece of plastic that is dark at one end and clear at the other – the dark part of the filter is positioned over the lighter portion of the scene, reducing the light variation (dynamic range) of the scene so that it can be captured without any loss of detail.
Drawbacks
As with other methods used to make your camera faithfully reproduce a scene with a wider dynamic range than it is capable of, ND grads certainly have their drawbacks:-
- The line between the clear and dark parts of the filter is a straight one (albeit with a slight fade/graduation to make it less noticeable). Rarely will a scene have a simple, straight line transition between dark and light so you end up having to compromise and perhaps hide the transition somewhere you hope the viewer won’t notice it
- Getting the gradient to start in the correct place takes a bit of practice – if it starts too low some of the foreground with appear slightly darker – if it starts too late the brightness of the sky might appear uneven.
- Like all lenses and filters they need to be kept clean – and as I swap them around between filter holders I have a tendency to drop them :(
With so many negative points, why use them?
Other methods of exposure balancing (such as exposure blending or HDR) require multiple exposures of the same scene, which realistically means using a tripod. I have a tripod, and I use it a lot, but I don’t always carry it – when I’m out with the family it’s an unnecessary burden – and sometimes I make the decision not to use it at all as constantly relying on it can lead to a lack of invention. A set of grads takes up very little room in my camera bag.
Processing time. Other techniques may only take a matter of minutes when you are skilled at them but if I’m taking an afternoon’s worth of casual shots I want them all to look their best with minimal editing.
An Example
These two shots, taken at sunset in Bradgate Park show the subtle but pleasing effect of using the Cokin P121M (ND4) grad. The first shot was taken without the filter. As you can see, the foreground is quite dark.
Technical info: ISO100, 18mm, f/22, 0.5s
The second shot (below), with the filter in place produces a much more even result.
Technical info: ISO100, 18mm, f/22, 0.6s
No further processing has been done to either image. As you can see from the technical info, the second shot was exposed for slightly longer (0.1s) which allowed more light from the foreground to be picked up by the camera sensor, resulting in a more even looking photograph.
