An Introduction to Neutral Density Filters
Neutral Density Filters (ND’s) are an essential bit of kit for anyone wanting to get right into their landscape photography. In particular, for sunrise and sunset when there is extremely high contrast (a very bright sky and a very dark foreground) the camera struggles as it simply cannot handle the “dynamic range”, that is, the range from the brightest white to the darkest black. In terms of your photography, this will result in images with either very bright and over-exposed skies; or nice skies but completely dark foregrounds with no detail at all.
While it is true (to a certain extent) that those dark foregrounds can be brightened in post processing, it is always good to do the best job possible in camera while you are out in the field. This is where the neutral density filters, in particular “graduated” neutral density filters, come in to play.
First things first – what is a neutral density filter?
Neutral density filters are a shade of black, and range from very light (eg 1 or 2 stops) through to almost completely black (10 stops). Neutral density filters are the same shade of black all over, and come as either circular or square filters. Basically they allow for longer exposures than would otherwise be possible by adding this dark layer to the end of your lens. The camera therefore needs to expose for longer to achieve an appropriate exposure.
Photographers use these filters particularly when water or clouds are present, as the long exposure provides a pleasing look as the clouds or water smooth themselves out over the course of the long exposure. 10 stop neutral density filters (or the “Big Stopper”) are quite dramatic whereas 2 stops is basically not very noticeable at all.
In my kit I have a 5 stop and a 10 stop ND.
So what is “graduated” all about then?
Graduated means that the filter isnt the same level of darkness all over and is great, almost essential, for sunrise and sunset photography. Just like ND’s, Graduated ND’s come in a variety of strengths (ie 1~2 stops generally through to about 8 stops). These filters will be dark at the top and will gradually become clear meaning you can position the darkest part of the filter over the brightest part of the scene (ie the sky) so that the filter has a strong effect at the top and a minimal effect at the bottom.
“Hard & Soft” ND Grads
There is one more consideration with ND grads – that of “hard” or “soft”. The difference being the way the filter transitions from dark to clear. In a “hard” ND grad, there is a rather definite cut off between dark and clear, meaning that there will also be a very obvious point in your photo where the filter cuts off.
“Soft” filters allow a gradual transition from dark to clear and therefore the result is much more natural and subtle.
There are many, many brands these days. Nisi have become very popular lately, and have stolen a fair bit of the thunder of previously popular brands. Cokin have been around a long time and have developed a very useful online explanation of the effect various ND filters have – click here.