The ND grad filter

ND (Neutral Density) grad filters are an essential addition to your photographic toolset if you plan to make serious landscape photography.

When to use a ND grad filter

A ND grad filter is useful in conditions where you cannot have both the sky and the rest of your image exposed correctly at the same time. When shooting in backlit conditions, the sky often turns totally white. This is especially true with digital camera as they have a far narrower useable f-stop range. You will therefore use a graduated grey filter to "hold back" the sky (make it darker).

Here is landscape taken without any filter. The sky is overexposed.

The same photo taken with a 2 stop ND grad filter on. The sky and meadow are properly exposed.

Which type of ND grad should you choose ?

Screw vs slide in filters

Some brands (for instance Tiffen) propose ND grads that screw on your lens, just like polarizing filters. I do not recommend these as you cannot adjust them vertically to move the filter area of effect.
Slide in filters are rectangular and made of coated resin. You generally need a filter holder to use them. Alternatively, you can simply hold them in front of your lens, when using a tripod.

Filter size

Slide in ND grads exist in two main sizes : Cokin P size is the one you are looking for if you are using a digital or analog SLR. They fit on the Cokin P size filter holder.
The larger (and more expensive) 4x6 size filters are suited for Lee holders and generally used on medium format cameras (or larger ones).

Filter density

ND grad filters exist in various densities to accomodate different lighting conditions. Depending on the brands, they can range from 1 stop to 5 stops. The denser the filter, the stronger the effect is (the skies turn darker). However, I do not recommend getting a full collection of them. 2 and 3 stops ND grads are the most useful ones. 1 stop will have barely visible effects, especially with a soft step filter (see below). You can stack two filters for more extreme backlighting conditions.

Filter stepping

You will generally have a choice between hard and soft step ND grads. You can see the difference below:

Hard step filters are useful when you have a fast transition between the sky and the ground. This includes when shooting a sunset at sea, for instance. They might be a problem when trying to hold back the sky on a landscape that includes trees or steep hills. You will see the darker area of the filter on any element that it covered by it, which will be avoided with the soft step one.

Using the ND grad filter

You will need this filters, when you face conditions where there is a lot of contrast between the sky and ground, generally in full daylight. For sunsets and sunrises, a reverse ND grad filter is more adapted.

Memorize exposure on the lightest area of the ground and slide in a filter with adapted density before taking the picture. To adjust the filter position precisely (especially when using soft step ones), press the depth of field preview button of your camera. If you are shooting at f/8 or above (typical apertures when making landscapes), the image in your viewfinder will turn darker and the filter's area of effect will be far more visible.

Sample photos

These photos would have been far less interesting or plain impossible to make without a ND grad filter.

Invalides courtyard

Flowing waters

Rolling meadows and white cows

Lone tree

Which brand to choose?

I started with an inexpensive kit made of a Cokin P filter holder with an adapter ring and a 2 step ND grad (the one above). I later switched to the more expensive Singh Ray filters, which have several advantages over the Cokin:

• Their more rectangular shape gives more range for adjusting the filter vertically
• Their color is more neutral while the Cokins show color shifts towards the red
• They are less sensitive to scratching, especially if you keep them in the provided pouch (which I strongly recommend)

Singh Ray filters are a bit of a luxury and no one would like to lose them. One day, as I was shooting in Brittany, a gust of wind took one off my hand and carried it away. It landed a few meters down a cliff, blocked by a small bush. I crawled down the cliff to recover it, holding mysleft to vegetation and getting fairly scratched in the process, but managed to get it back!

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