It is very common for me hear this question from beginners in landscape photography, "I want to invest in graduated ND filters, but I don't know when and how to use them?". This article will deal with whenand how parts, let's start with some basics.

Types of Graduated ND filters

There are a few types of Graduated ND filters available through various manufacturers, but the common and most widely used ones are a soft graduated ND filters and a hard graduated ND filter. NiSi filters, for example, also provide reverse graduated ND filters and horizon graduated filters as part of their kits.

Hard Graduated ND Filter: It blocks equal amount of light from top to the center of the filter. The transition in the middle of the filter is abrupt i.e. the dark part of the filter ends suddenly into the lower half of the filter, which is clear.

Soft Graduated ND Filter: Its filtration of light is dense on the top, but it becomes gradually soft as you move towards the center of the filter. In other words, the transition from dark to light is not abrupt. The lower half of the filter is clear, it blocks no light.

You can use these filters in various combinations, even by stacking them on top of each other, but I will illustrate more simple uses of them. I leave it up to you to do more practice and figure that out for yourselves.

Why we use a graduated ND filter?

While taking landscape photos, especially around golden hours, to capture the right amount of light in the foreground and background of your images becomes quite tricky. If you expose correctly for the elements in front of you, the sky gets over-exposed (or too bright), and if you get the perfect light on the sky in your shot, the foreground becomes under-exposed (or too dark). This is called a scene with "high dynamic range scene", and you will hear it often from landscape photographers.

The filters help you block light from certain portion of the scene so that you can get the right exposure in one shot. You must shoot in manual mode when using graduated ND filters, this way you will have full control of the shutter speed.

When to use a Hard Graduated ND filter?

The ideal situation for using a hard graduated filter is when the horizon is straight. I have mostly used a hard grad when shooting seascapes. Looking towards the sunrise or sunset, the ocean meets the burning sky in a straight line, and that suits the shape of the hard transition from dense to clear in the filter. If there are no mountains, boulders or other big elements like trees, then keep the hard part of the filter, i.e. the dense part that blocks the light, on the sky, and the clear part on the ocean. The reason you want to do that is because generally the light on the sky is 2 to 3 stops brighter than the light in the foreground. My advice would be that you shoot in manual mode when using graduated ND filters. I used a hard grad to take the following photos, the filter's clear part was placed on the foreground and the water, and the dark part was on the upper potion i.e. the clouds and the sun.

When to use a Soft Graduated ND filter?

There are a few reasons why you would want to use a soft grad. The first would be the opposite of a hard grad i.e. the horizon in not even. If, for example, there are mountains in your scene, and you use a hard grad to get the exposure on the sky right, the mountains will also become dark if you placed the dense part on the mountain. Placing the dense part of the soft grad on the sky, and the less dense part on the mountains will give you much smoother transition. Or, you might only want to put the less dense part just above the mountains and more dense part on the upper most portion of the sky. Again, my suggestions would be that you shoot in manual mode when using graduated ND filters.

I used a soft grad for the following image, the less dense/soft part of the soft grad was slightly placed on the mountains.

A soft grad was also used to take this seascape, but the filter was placed on an angle. The only bright part in the sky at the time of taking this shot was the left area with clouds, the foreground and the arch shape mountain were relatively less bright, and only a small portion of the dense part of the filter was on the mountain and the water. The image was shot in manual mode.

When is it better to not use Graduated ND Filters?

Sometimes it is best not to use a filter and do exposure bracketing/blending. Exposure bracketing is also known as HDR or image composite. It is a technique in which you take multiple shots, at least two, to get the full dynamic range of the same scene. The image below is not my favourite, but it is a good example of a tight composition where everything was on top of each other. The sunrise was extremely bright but the valley was in dark shadows. There is not much sky in my composition either, and putting in a soft or a hard graduated ND filter was just not feasible. So I ended up taking two images, in the first image, the sky was rightly exposed, and in the second image, the foreground was exposed. I blended the two images in Adobe Photoshop later for the final image. Some photographers don't use filters at all, they prefer exposure blending, it is a personal preference.

How to use graduated ND filter?

What I am about to tell you is something I don't practice anymore, I guess I have applied this rule enough number of times to now subconsciously put filters and adjust my shutter speed. So let's suppose you want to take photo of a scene with high dynamic range i.e. there are very bright areas in the sky, and very dark areas in the foreground. Also assume it is a seascape and you want to use a hard graduated ND filter. Focus on the brightest areas in the sky, and note the shutter speed in aperture priority mode. Then focus on your point of interest in the foreground in aperture priority mode and note the shutter speed. Let's say that the reading for the background was 1/250th and the foreground 1/30th of a second. The difference between these readings is 3 f-stops and for the purpose of taking a photo, you must use a 3-stop filter. If you don't have a 3-stop filter, a 2-stop filter will also do (roughly, you can do some post processing later). Put the hard part of the graduated filter on the sky, and the clear part on the foreground. You must now shoot in manual mode and your shutter speed must be 1/30th of the second. Easy...

Muji

Why, How and When to Use Graduated ND Filters