The second part of this series is about neutral density filters. There are several variants but all have at least a portion of the filter that is darkened. This area reduces exposure by a number of stops depending on how dark the filter is. The ‘neutral’ part refers to the theory that the effect is without any colour cast. The true degree of neutrality differs between manufacturers. The more expensive brands like Lee, Hi-Tech and Singh-Ray tend to be more neutral. I have a preference for Singh-Rays because their filters come in a wide range of accurately stepped strengths and their very neutral effects. Cokin make a neutral gray filter series which are more easily accessible at stores and considerably cheaper. However, a magenta colour cast is quite common with these.
Editor's Note: Thumbnails are links to larger images
These come in the circular screw-on variety to attach to the lens thread just like polarizing filters. They also come in rectangular shapes designed to be slotted into dedicated filter holders. Both types work well but if you plan to shoot very long exposures with multiple filters, the rectangular ones would be a better choice.
The entire filter is uniformly darkened to reduce exposure of the whole scene, allowing for longer shutter speeds. Why would anyone wish to lengthen exposure time?
Personally, this is my least used filter since my polarizer doubles as a 2 stop neutral density filter. However, many landscape photographers use them very effectively in adding drama to their work.
The rest of this article deals with the use of graduated neutral density filters (GNDs). I consider them essential in photographing scenes during the hours that lie either side of sunrise and sunset. While these are low-light situations, the contrast of a shadowed foreground against a relatively bright sky is too great for a digital sensor or most films to capture.
GNDs are rectangular filters which are clear on one half and dark on the other. The dark half of the filter is positioned over the bright part of the scene to enable both the sky and ground to be the correctly exposed. This is the reason that the circular screw-on GNDs should be avoided as there is no flexibility in the positioning of the grad line.
GNDs come in various strengths which are measured in the amount of stops the darkened portions of the filter reduce the exposure by. The most commonly used are 2 and 3 stop filters.
This refers to the way the filter transitions from clear to dark. For instance a 3 stop hard GND will abruptly go from 3 stops of darkness to clear in the middle of the filter. This ‘hard edge’ is useful for landscapes with a straight horizon such as looking out to the sea. A 3 stop soft GND on the other hand, will be 3 stops darker at the top and gradually becomes lighter as it approaches the centre where it transitions to clear. Filters with a soft gradation are useful for horizon lines that are complicated by treelines, mountains, buildings, etc.
Although I prefer to hold filters in front of the lens by hand most of the time, I still recommend investing in a filter holder. This usually has at least two parts
Lee makes the Rolls-Royce version, beautifully built with various configurations and accessories, including a ring that allows a polarizer to be attached. Cokin also manufactures a range of holders. These are less impressively built but cheaper and work well enough for my purposes.
I will spend some time describing the P-series Cokin filter holder. These are the most readily available and popular. They are available in a standard size which have slots for 3 filters or a wide-angle version with a single slot for one filter only. While I’m sure anyone who invests in the Lee or Cokin’s X & Z series holders will get great use out of them, my personal preference is for the P holder for the following reasons :
The savings in cost and space come with a very significant disadvantage however - external vignetting. On wide angle lenses, the edges of a standard filter holder will be visible in the frame up to a focal length of 24mm on a full frame camera. To deal with this problem you can buy a wide-angle version that has a slot for only one filter. This will cause external vignetting up to 18mm. Since I often stack my GNDs, I also own a standard P-holder with the third slot sawed off so it can still accommodate two filters. This vignettes to a focal length of about 22mm. Since I handhold grad filters 95% of the time I find the external vignetting at the ultra-wide end an acceptable compromise to using the Cokin P-holder. (See photos of filter holders with slots sawn off to accommodate 1 and 2 filters).
If you prefer to use a filter holder all the time and shoot focal lengths wider than 18mm frequently, the larger Cokin systems (X & Z) or Lee may be a better solution for you. Lenses with an 82mm thread (such Canon’s 16-35mm 2.8L MkII) or larger will not fit the P system either.
This technique may not suit everyone. Some will find that no matter how hard or which way they try, the filter can’t be held steady enough in front of the lens. This will cause incorrectly aligned grad lines and blurred images from camera movement. I think it is a technique well worth attempting to master for several reasons.
Most people develop a handholding technique for themselves but I have provided some photos of what works for me. Obviously the camera be secure on the tripod and shouldn’t move if tapped. The GND then needs to be held directly against the lens. This prevents light reflecting off the filter into the shot. I hold the filter with my left hand and hit the shutter via a cable release in my right. (See photo of handholding technique). I can usually hold the filter steady for 15 seconds in the one hand. For longer exposures than this I use the self-timer and a two-handed technique for extra stability. (See photo of 2 handed technique). Anything more than a 30 second exposure really requires a filter holder. If you find that you cannot handhold don’t worry, many of the best photographers in the world will only use holders.
GNDs are usually necessary for any scene where the foreground is in shadow and the sky is relatively bright in comparison. Almost all landscapes taken within an hour either side of sunrise and sunset will fit this requirement. You can determine the difference between sky and shadowed foreground formally using the camera’s spot meter. Most digital cameras are able to capture a usable range of 6 to 7 stops. If the exposure difference is greater, you will need to use a GND to compress the dynamic range of the scene. This is the traditional way of doing things.
I find a simpler method is to spot meter the foreground with something to be rendered as a midtone then make an exposure. Check your camera’s LCD. If the sky is blown out using your highlight indicator or histogram, you’ll need to use a GND. Yes it is sometimes possible to underexpose the foreground and get the sky to fit into the camera’s dynamic range without the GND. However post-capture lightening of an already dark foreground that is under-exposed is a recipe for creating noise. Getting all parts of the scene correctly exposed in-camera using filters yields cleaner results.
If you have accurately determined the difference in stops between the foreground and the sky by metering both, you’ll be able to choose an appropriate strength of gradation. For example, if there is a 10 stop difference between the sky and the ground, a 3 stop GND will be needed to compress the range to 7 stops, which the latest digital sensors should cope with.
These days I rarely have to spot meter the scene formally. I use matrix metering mode without the GND then use the filter I think will do the job. With experience you will be able to reach for the correct GND gauging the light differential by eye. You can start using this method now with these rules of thumb.
The next decision is whether you use a hard or soft GND. This will be determined by whether there is a clear line between light and dark. If so the hard edge will be the best option. Note that if the hard edge of a 3 stop hard GND passes through any dark area it will likely become a clipped shadow. Retrieving any detail from this will be difficult or impossible.
Try to envisage what parts of the photo you find acceptable to go to pure black or white. The darkest part of a deep shadow may be okay clipped, just as sun on view is often allowed to become a clipped highlight. These are personal artistic decisions you get to consider and make.
The grad effect varies depending on the aperture. It is important to use the depth of view preview to check this when putting the GND in place.
My philosophy is to get the shot as correct as possible at the time I press the shutter. This is why I carry the following GNDs on all my landscape trips : 1 stop hard, 2 stop hard and soft, 3 stop hard and soft and a 4 stop hard. In addition to this are reverse GNDs (to be covered in part 3 of the series) in 2, 3 and 4 stops. I find it more convenient to bring these 9 GNDs into the field than have to spend more time processing on the computer later. It is also a lot more satisfying to get the shot exactly right ‘in-camera’.
Of course I wouldn’t suggest running out and buying the same selection of GNDs. A basic set (as used by Galen Rowell) is considered to be : 2 stop hard, 2 stop soft, 3 stop hard and 3 stop soft. This set-up gives you the ability to expose for almost any lighting situation.
Only want to try out a single GND first? The 2 stop hard filter would be the best choice here as an all-rounder. Want to stick to just a couple of grads? I would recommend a 3 stop hard and 2 stop soft combination if you shoot a lot of seascapes. A 3 stop soft and 2 stop hard would be more suitable for mountainscapes.
Keep in mind that there is often more than one way to filter a scene; a 2 stop hard may work just as well as a 3 stop soft for that lake scene. You may make exposure and achieve a good histogram with either method. Or perhaps a combination of 2 filters can also work. There will be subtle differences in these results and it is up to you to experiment and learn which suits your artistic vision.
Freycinet National Park, Tasmania, Australia
Canon 5D, 16-35mm 2.8L, f16, 15 seconds, ISO 200, tripod, 3 stop hard Singh-Ray GND
This is a straight forward use of a GND. The sun had set about 20 minutes before this shot, directly in front. Although it was a low light situation, the sky was relatively a lot brighter than the foreground in shadow. The horizon is essentially straight and I was shooting into the direction where the sun had set so a 3 stop hard grad was an easy choice. The arrows show where the grad line was placed.
There is a peculiar issue that occasionally affects the combination of ultra-wide focal lengths, P-Cokin filters and vertical compositions. Light can reflect off the top of the filter and cause lightening in the top corners of the image. Handholding the filter in these cases eliminates the problem. That was the reason I increased the ISO to 200 to enable a shutter speed of 15 seconds which is the maximum time I can hold a filter steady.
Mount Ossa, Tasmania, AUSTRALIA
Canon 5D, 16-35mm 2.8L, tripod, f22, shutter 0.3 seconds, ISO 100, Singh-Ray 2 stop hard GND
This one was taken in the mid-afternoon, not during the magic hours. A GND was needed because of a foreground in shadow and a sky that was bright with numerous clouds. The sun was behind me so a 2 stop GND was used. Although not perfectly straight with several peaks in the distance, the horizon line was even enough to use a hard grad. Note that there is a darkened area on the left where the grad part of the filter has passed though some land. This is known as a grad line or shoulder. Provided the scene is not underexposed some detail is usually retrievable with post capture processing if a 2 stop GND was used. If you use a 3 stop GND be prepared not to get any detail out of these darkened shoulders. Some advanced techniques to avoid this will be discussed in the next article.
Sunrise at the Twelve Apostles, Victoria, Australia
Canon 5D, 16-35mm 2.8L, ISO 200, f22, shutter 3.2 seconds, tripod, 2 stop soft GND
There was soft lighting with the sun about to rise behind me. The 2 stops of filtration was used to darken the sky, maximising the pastel purple hues. The sea stack and cliff interrupted the line of the horizon so a soft edge GND was chosen to avoid darkening these structures excessively. It was important to keep detail in the stack and cliff for the scene to look natural.
The third and final article will discuss more advanced GND techniques such as stacking and reverse GNDs.
Kah Kit Yoong is a self-taught Melbourne-based nature and travel photographer who is always in search of the perfect light to suit his subjects. He took his first snap with an SLR almost three years ago then developed his skills photographing the wild landscapes of Tasmania. In addition to his fascination with historic Italian towns his travels have taken him to New Zealand, France, Hungary, Slovenia, Croatia, Switzerland, Austria , China and most recently, the Canadian Rockies. Kah Kit’s work has been published in Popular Photography, the ANZANG Nature and Landscape Photographer of the Year 4th collection yearbook and various Canon publications.
More of Kah Kit's work can be found at Magic Hour Travelscapes
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