Have you ever taken a photograph of what you think will be a gorgeous landscape only to find the sky is completely white with very little, or even no detail, like this?

In this photo the foreground is perfect but we've lost detail in the sky. So we do the obvious, shorten our shutter speed to allow less light in so that the sky isn't too bright. Now we get a photo like this:

I'm happy with that sky, unfortunately what we've now got is a foreground, the lovely Ashness Bridge near Keswick in the Lake District, that is way too dark.

This is a common issue for landscape photographers, the scene contains more dynamic range (that is to say the difference in brightness between the darkest foreground and the brightest sky) than the camera can record. The difficulty is that your eyes are much better at making the most of a scene like this than even the best cameras. 

What we need to do is to somehow balance the brightness of the sky and the darkness of the foreground so that both are recorded in the same shot.

One way is to blend both images in Photoshop. This would certainly work in a photo like this where the only movement in the shot is the water. If however there was a few elements moving, maybe waves rolling into a seascape, or any scene with people in them it becomes a lot more difficult to get a convincing result. 

I, and a lot of other landscape photographers, prefer to get as much done in the camera as possible, after all, I'd rather be sat watching the sun come up over Skiddaw on a lovely crisp winter's morning than sat in front of my Macbook in Photoshop trying to make it look right. The answer for us is Neutral Density Graduated Filters, usually abbreviated to ND grads, or just grads. These filters are dark at the top and light at the bottom, allowing you to balance the brightness of the sky against the darkness of the foreground, in one shot.

So, how would we balance out a shot like this?

Sunrise Over Skiddaw, At Ashness Bridge I used a 3 stop graduated neutral density graduated filter, applied over the sky and mountains in my photograph. This brought the brightness of the sky down to a level where it could be recorded by the camera. With this photo I also used a circular polariser to cut through reflections in the stream, this is best seen in the pool to the bottom of the image;

Sunrise Over Skiddaw, At Ashness Bridge I favour a British made brand of filters from Lee, an old name in the film and photography industry. Their filters are hand dipped (in the dye) to ensure the best quality. Their Quality Control is rigorous which means that there is sometimes difficulty in getting supply of them; it is worth waiting for them, I've tried all the brands and whilst Lee aren't cheap, they are the best.

So, what do we need? Rather than just send you off to find these I'll link to them at our friends Dale Photographic in Leeds who are one of my closest suppliers of Lee filters.

You will need the following:

1. A filter holder. Lee call this their Foundation Kit. It has multiple slots so you can stack multiple filters. 
2. An adaptor ring for each lens you want to use filters on. At the end of your lens there will be a guide to its filter size, usually indicated with a symbol like an O with a strike through it. As a guide my Canon 17-40 takes a 77mm filter whilst my Canon 24mm TS-E takes a 72mm filter. If you're going to use filters on a wide angle lens (as is often the way with landscape photography) I would recommend the wide angle adaptor rings.
3. The filters themselves.  Filters come in a range of strengths, from 0.3 (one stop) through to 0.9 (three stops). I personally would avoid a one stop, I've not found much use for those. I mainly use a three stop, living in North Yorkshire where the moors are dark coloured heather, and travelling to Scotland with dark coloured rocks there is often quite a big difference between the foreground and sky. Next you can choose between hard and soft edged grads, this refers to how quickly the filter changes from the dark to the light side. I prefer to use hard edged filters for the majority of my shots, I find that with a soft edged grad only the very top of the filter is the stated strength, that can lead to a band of blown (pure white) sky above the line of hills or mountains you're photographing. If you want one filter to start with I'd get a 3 stop hard edged and see how you get on.

So, we've got all the kit, how do we use them? First we've got to work out the difference between the sky and the foreground. Put your camera into spot meter mode, aim at the foreground in aperture priority mode and see what the reading is and remember it. As an example say the camera told you you would need 1/30th at f11. Now aim at the sky and take another reading, imagine this reading is 1/500th at f11. That means there is four stops difference between the sky and the foreground (one stop would be 1/60th for the sky, two stops would be 1/125th, three stops would be 1/250th and four stops is 1/500th). I usually take one away from this figure, to allow for the sky naturally being brighter than the foreground. As such I would use a three stop filter to balance the scene.

Now align your camera (hopefully on a tripod, and using a cable release) to get the composition you want and make sure it is level. In manual exposure mode set the camera to the setting you had for the foreground (1/30th of a second at f11). Focus and switch the lens to manual focus so that you don't knock it as you apply the filter. Now switch on liveview if your camera has it, and, watching the screen, slide the filter into its holder on the front of the lens. If you press the Depth of Field preview button on your camera it will really help show where the gradation lies. Align the gradation with the horizon. Now trigger the shutter with your cable release to take the shot. Check the histogram on the screen of your camera to make sure you've applied enough filtration, there should be a gap at the right hand edge showing you've not blown the highlights. Most cameras have the option of highlight warnings, or blinkies, to tell you where a shot is overexposed to the point of losing detail, these are invaluable.

In time you'll get used to just looking at a scene and in your head working out which filter you want, this just comes with experience.

I hope this gives you a brief starting point with filters, they really are, in my opinion, an essential tool for the landscape photographer. If you have any questions feel free to email me through my website, I'll do my best to help.