How to use a Graduated Neutral Density Filter

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Using a Graduated Neutral Density (ND) Filter:

What they are and why you need them

For beginning photographers, there comes a pivotal moment to understanding the limitations of how much can be recorded on film or with digital sensors. This moment came for me on a road trip where I came upon a great sunset. Beautiful colors, vibrant green hillsides, cows munching . . I wanted to capture this moment. I pull over and snap the picture with my new fancy camera. Not sure how to work all the settings, I just let the camera decide on exposure. The next week I see the results of my effort when I get the film back. Disappointing!

The sky was close to what I had seen (the camera was pointed up enough so that it metered from the sky) but the beautiful pasture and cows were only a silhouette. This was my first visual lesson that film (and digital) cameras can only reproduce a 3 to 4 stop difference in lighting.

An example of how this may occur for a typical sunset goes as follows. You point the camera up to meter off the sky. For a given aperture, the shutter speed is indicated as 1/500s. You then point the camera down to meter the foreground and read 1/30s. This represents a 4 stop difference in exposure. (counting down from 1/500s: 1/250s, 1/125s, 1/60s, 1/30s) The guessing game then starts, what do I set the exposure to? 1/500s will get you a great sky with a silhouette for the foreground. 1/30s will give you detail in the foreground, but the sky will be "blown out" with the vibrant colors replaced by drab gray or white.

Settling for a middle exposure of 1/125s doesn't work well as nothing looks good. There are several techniques for dealing with this issue, and one of the best is using a graduated neutral density filter. Neutral Density (ND) filters are somewhat like sunglasses for you camera. Good ones simply reduce the quantity of light entering the lens (with little color shift). A graduated ND does just as it says - the portion of filter that is dark is graduated over it's surface with half being clear, the other half being dark, and a portion between being a smooth transition between the two.

There are several decisions to make regarding what type of graduated ND filter to choose. First is the type. You can get a graduated ND filter in a round shape that screws onto the front of your lens. You can also get the graduated ND filter in a rectangle that fits in an adaptor that attaches to your lens. I can't comment on the round type as I have never used one. The reason I discounted round ND grads is that you can't change where the transition from dark to light occurs in your framing. If you always take pictures with the horizon in the dead center of your frame, then you may be in luck. For the rest of us, go with the rectangular variety. In my experience, being able to set the transition area precisely greatly increases your options in composition.

The next decision is how dark do you need the grad ND to go? The filters are usually sold in 1 stop increments where a 0.3 ND will reduce the light entering by 1 stop. A 0.6 reduces by 2 stops, 0.9 by 3 stops, etc. The example above would in theory require a 1.2 ND grad (4 stops). I say in theory because there are times that you do not want to balance the foreground and background exactly - you may want the foreground to be 1 or 2 stops darker than the meter indicates as this may make your picture more natural looking. It is best to experiment with 1 filter under different circumstances to see if the results are too obvious. Since ND grads are sometimes not offered in a 1.2, you would settle for a 0.9 to reduce the sky exposure by 3 stops.

Shown below is an example of what filtration can do for you. It is not scientific and far from perfect as the exposure was not exactly the same for both - the foreground is a little darker in the example with the filters. It is also is not only a demonstration of the ND grad as I also added a polarizing filter.

Without ND filter

This picture from Puerto Rico was taken with no filtration. The detail is good in the foreground but the sky is a total loss of detail.

Same setup, same time of day, but this time I used a polarizing filter along with a Hitech 0.6 soft ND grad. Again, this example is not perfect because I lowered the exposure slightly as you can see with the darker foreground. Rest assured that most of the detail gained in the sky is from the ND grad. I positioned the transition on an angle to match the contour of the wall.

I mentioned in the description above that I used a soft ND grad in the example above. This brings us to item #3 to decide on. ND grads are sold in "soft" and "hard" varieties. This refers to the transition area between dark and clear. A "soft" ND grad will have a longer (more gradual) transition area between the two while a "hard" will have a shorter and more abrupt transition.

If you are taking a picture of a sunset with an entirely flat horizon (such as in Amarillo Texas), then the hard variety will be better as it will allow you to transition quickly and match the contour of your subject. If, however, the transition between light and dark in your subject is more irregular (like the example above) you are much better off with a soft ND grad.

Hitech 0.6 vs 0.9 neutral density graduated filters

The illustration above shows differences between two ND grads that I use. On the left is a Hitech 0.6 soft and on the right is a Hitech 0.9 hard. You can see the 1 stop difference in that the 0.9 on the right is darker. Also notice that the transition area is longer on the 0.6 soft on the left.

Here are a few quick and dirty tips for how to use your ND grad filter:

First meter off the sky, then meter off the foreground to see what you are working with. Even if you don't have a spot meter (either separate or built into your camera) you can make do by selecting center weight metering and making sure to aim the camera high (and then low) enough to encompass all of your subject.

Next, determine what strength of filter to use. This will be dependant on what filters you have available. Don't think you need to buy all of them. In fact, I would recommend you just choose one and learn how to use it. If your metering determines a 5 stop difference and you only have a 0.9 (for 3 stops) use it and see what happens.

Err on the side of under correcting rather than over correcting. If you use too strong of a ND grad, you will end up with sky that looks dark like the last light of evening and a foreground that looks like the middle of the day. If this is the effect you are looking for, then go for it! However, know that this may appear unnatural. Gaylen Rowell was notorious for going a little overboard in using ND grads that were a little strong and left the foreground very bright. Having said that, all the examples I would complain about are leaps and bounds better than I have ever taken, so go with what you feel will give you the best results.

Err on the side of positioning the transition too low. You usually want the sky in your composition completely covered by the dark area of your ND grad. If the horizon is uneven, this will mean lowering the filter so that the lowest point is completely covered or the filter is set at an angle. If you set the ND grad too high, it will leave a stripe of blown out sky just above the horizon. This looks very unnatural. For a sunset shot, the region that needs held back the most is the area right over the horizon (where the sun is) so you want to make sure it is covered.

Seeing where the filter transition occurs through the lens can be difficult. To make it easier, use the following method: Set the lens to a small aperture, around f16 or f22. With one hand, stop the lens down by holding down the appropriate lever or button. While looking through the lens, use your other hand to wiggle the filter up and around. You will be able to clearly see the transition region moving around. Keep the lens stopped down and slide the filter to completely cover the sky. Make sure to readjust your aperture if necessary before taking the shot.

I would encourage anyone learning about photography to take the jump and use this amazing tool. To begin with I would recommend the following setup for most 35mm or digital setups:

Cokin P type holder and the appropriate adaptor to screw on the front of your lens. The P size is a great compromise that will cover most focal lengths you will use.

Hitech 0.6 soft ND grad. I struggled with the decision between soft and hard. I use the soft filter much more often. Very few compositions are straight enough to confidently use the hard ND grad. The soft is easier to use and will often give more predictable results. 2 stops of correction is good for most pictures that I take. The most vibrant colors usually occur when the sun has gone down and the sky is a bit darker. At this time, 3 stops is sometimes too much and the 2 stop (0.6) is perfect.

A stronger ND grad, such as the Hitech 0.9, is a good next addition. I chose to go with a hard transition for the 0.9. It works well for some sunset shots, but I generally find I reach for the 0.6 more often.