Whether you do landscape photography, or you’re a street photographer, there will be times where you are capturing a scene that isn’t exactly perfect. This is where a Neutral Density or ND filter comes into play.
If you are that photographer who wants to remove the people from the scene, then read this first. Stay with us here if you want to know when, where and how to use an ND filter.
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What Are ND Filters
A Neutral Density or ND filter is a piece of glass that reduces the amount of light hitting your sensor or film plane. They sit in front of your lens and come in three different types, in three different styles.
A normal ND filter has a coating that covers all of the glass or plastic element that you photograph through. The best ND filter affects everything in your scene.
To use them, you place them between the light source and your digital sensor or film plane. This could mean clipping one in between your digital camera body and lens, or on the front of your lens.
Using an ND filter is easy, you just attach it and shoot. Knowing when to use them is the tricky part. Let’s look at an example.
How To Use a ND Filter
Let’s say you are photographing a lighthouse, with the sea in the background. Your camera settings could be something like this: ISO 100, Shutter Speed 1/1000 of second and an Aperture of f/8.
The scene is well exposed, but the waves in the background are a little distracting. We want to smooth them out. And to smooth them out, we need to turn the scene into a long exposure.
This will record the scene over a period of seconds, stopping our camera from freezing the movement of the water.
We need a shutter speed of 15 ” (seconds), so we change the shutter speed on our camera. Except now, we have added 14 stops of light into our scene, meaning it is now just a white, blank image.
For a correct exposure, we need to take out 14 stops of light using the other settings.
The ISO is at its lowest, so that won’t help. The shutter speed or f-stop can go from f/8 to f/11, f/11 to f/16 and f/16 to f/22. That is only three stops until we reach our maximum (four if you can go to f/32 or ISO 50). So what about the other 11 stops?
The best ND filters come in many different strengths, and they compensate against this abundance of light. For this purpose, we need a 10 Stop ND filter. We can’t get exactly 11 stops, so the extra stop will have to be corrected using editing software.
Our light has been brought back down to a usable strength.
What Are Variable ND Filters
A variable neutral density filter or variable ND filter is a filter made from two separate pieces of glass. These two pieces of glass are polarised. One is linear, the other, circular.
You twist the ND filter to offset the polarisation. Polarized at a 90-degree angle, the filter lets in zero light. at 0 degrees it lets in 100% light.
Having polarizing filters such as these means you do not need 10 seperate filters as all of them are present in one handy system.
However, we do not recommend these as they are incredibly expensive. They also introduce artifacts into the out of focus areas and you will find you will not need this many ND filters.
When to Use a Graduated Neutral Density Filter
A graduated ND filter is slightly different from a ND filter, but the idea stays the same. The graduated part comes in as these are filters with a 50% ND coating.
They start halfway up, and gradually get stronger, reaching full ND filter at around two-thirds of the way up.
A graduated ND filter is for darkening a specific part of the image, not the whole scene. Skies are the main use, as the sky can be 3+stops lighter than the well-lit ground underneath it. Here, you darken the sky and not the ground.
They are graduated to make the transition from ground to sky a lot smoother. If it wasn’t graduated, the separation line would be very obvious, ruining a perfectly good image.
They can be rotated if the lightest element is in the bottom half of the frame.
Likewise, if only the top third of the image is too bright, the filters can be moved up or down to compensate. They come in the same strengths as the ND filters.
What Are the Different Styles of ND Filters
- Slide-In. The slide-in version of the ND filter requires an adapter or filter holder. This fits or screws on to the front of your lens, and once attached, you can slide the glass into it.
- Screw-On. The screw on version is threaded, which allows you to screw it on to the front of the camera lens.
- Clip-In. There are types of ND filter that sit in your camera body, just in front of your mirror. These are preferable, as they do not refract light like the others could.
What Are ND Filter Strengths
These filters come in all different strengths, for all different sorts of situations. When we talk about strength, we think in terms of stops. A 2-stop ND filter stops twice as much light as a 1-stop filter.
We use stops to make the transition between camera settings and filter easier.
A stop in photography is either halving or doubling the amount of light. In the case of ND filters, you are always halving or reducing the amount of light. A 1 stop ND filter will be stopping the light by 50% or half.
A 10 stop filter is stopping the light by 10 halves in a row. It is important to do this sequentially.
Some filters might be advertised in different ways. For example, instead of saying stops, they might use Optical Density of `1.5’ or a ‘ND factor of 32′.
When you’re capturing long exposures it’s only the shutter speed you will change. If you have a 12-second exposure without a filter, then you add a 1 stop ND filter, you have effectively halved the amount of light.
To counterbalance this, you have to increase the amount of time you let light into the camera, in this case by doubling it. 1 second becomes 2 seconds.
See the below table for all ten examples. The new exposure times double sequentially. So a 4-stop ND filter will mean you have to double the original exposure 4 times.
When to Use a ND Filter
If you come across a body of water and want to create that glass effect, you need the water to be fairly still. Allowing a few clouds to creep overhead will give your sky detail.
Midday with bright light will be too hot to photograph, even with the best ND filter, so try to aim for sunsets and sunrises.
We recommend getting the 6 stop and 10 stop ND filters. They will cover the majority of what you want to use them for, and give you a good workable base to buy others in the future.
What Other Equipment Will You Need
There will be other equipment you will need to use alongside the best ND filters. for one, you need an adapter is you are going to use the slide-in type. Also, a tripod will be needed for long exposures regardless.
A cable release or remote trigger is also important, as it means you will won’t need to touch the camera physically. This will reduce the amount of camera shake and blurriness in your image.
The camera setting ‘Bulb’ is something that can be really handy here. You’ll find that your camera will not have shutter speed than goes longer than 15″ or 30″. Bulb mode will let you open your shutter for as long as you need.
DIY ND Filter
There are many articles on the world wide web looking at cheaper solutions for the best ND filters. There is one thing you can use, but where you save on cost, you spend on time.
A welders glass is the thing that most DIY photographers use that offers them the reduction in light. They are a fraction of the cost, but, as I said, they will require you to do a lot of colour management editing.
These pieces of glass can leave colour casts on your images too difficult to eliminate. They will give you 10 stops reduction in light, and if you are interested, read this article here on how to process the final image.
Best ND Filter
At Expert Photography, we get to play around with many items hanging around our studio. I had previously bought an ND filter pack from Amazon that I was really looking forward to using. This was before I did any professional research.
The pack I bought was the Rangers 8pcs ND Filter Kit. I finally got it, and went out to try it. This is what I tried to use on our How to Use an ND Filter to Remove People from Long Exposure Shots article.
From looking at the problems, these ND filters may not be strong enough on their own, and stacking with these filters are not good. They are plastic and will give your images a vignette, a coloured tint and a higher possibility of refracted light.
So instead, I went with Lee’s Big Stopper. This is an ND filter with a 10-stop reduction in light. Wow. It won’t be enough for a solar eclipse (you’ll need two of these) but it will help in your landscape or street photography.
On a serious note, these ND filter aren’t cheap – but here, you get what you pay for. If you are going to use it a lot, then there is no question – Lee’s Filters are the way to go.
What to Do About Common Problems When Using ND Filters
There are problems that I found from using ND filters before. I would recommend getting mid-range glass ND filters. The Rangers 8 pc ND filter kit is a plastic version and gave me a purple colour cast and a hazy final image.
Also, do not try stacking the filters. I know it is tempting to put a 4-stop ND filter and a 6-stop ND filter in replacement of a 10-stop ND filter.
What it will do is cause light refraction, where the light entering will bounce between the two pieces of glass, showing you dust and light spots.
Also, vignetting will occur as the light now hits your sensor from different angles. And if they give you a colour cast, putting two together makes it twice as bad and more difficult to remove.
We have a great guide to camera lens filters you can check here. For more on using ND filters, check out this video.