There will be times where you need to capture scenes that are too bright for the camera. In these situations, Neutral Density (ND) filters come into play.
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What Does an ND Filter Do?
Neutral Density or ND filters may sound too technical to use for a beginner photographer. To make it easier to understand, you can think of them as sunglasses. All they do is reduce the amount of light hitting your sensor or film plane.
You can attach the filters in front of your lens like any regular filters. If they’re round, you can screw them onto the threads of your lens. And if they’re square, you can slide them into a filter holder.
For the most part, using ND filters is easy. But knowing when to use them is the tricky part.
Why Should You Use ND filters?
The scene is well exposed, but the waves in the background are a little distracting. We want to smooth them out. And to do that, we’ll need to do a long exposure.
A long exposure records the scene over 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. So it’s now just a white, blank image.
For 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’s only three stops until we reach our maximum (four if you can go to f/32 or ISO 50). Not to mention that it if you go above f/16, you might see a diffraction effect resulting in unsharp images.
So what about the other 11 stops?
For this purpose, we need a 10 Stop ND filter. We can’t get precisely 11 stops, so we’ll need to deal with the extra stop using editing software. But with this combination, we can finally create proper exposures.
When Should You Use a Neutral Density Filter?
There are plenty of situations you can use the neutral density filter.
In portraiture, using this filter would allow you to shoot with a wide aperture even in the middle of the day. That way, you don’t have to end up with images with ugly highlights.
And for architecture photography, you can use it to “erase” people in the scene. Since people move around, they won’t show up in your photos if you do long exposures. You can learn more about this technique by reading this article.
To use filters ND kit, you’ll have to figure out how much light you have to cut out first. If there isn’t enough light, then perhaps putting an ND2 filter should be enough. But if your image still looks overexposed, then perhaps you can try an ND4 or other options until the lighting looks correct.
If you’re using a variable ND filter, all you have to do is twist it until you get the correct exposure. It’s that easy!
What Are ND Filter Ratings?
ND filters come in all different ratings for all different sorts of situations. When we talk about exposure, 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 either doubles or cuts the amount of light in half. So that means a 1 stop ND filter cuts the light by 50%.
A 10 stop filter is stopping the light by ten halves in a row. It is essential to do this sequentially.
Companies advertise filters in different ways. For example, instead of saying stops, they might use the Optical Density of `1.5′ or an ‘ND factor of 32’.
When you capture 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 one-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. One 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 initial exposure four times.
What Are the Different Types of ND Filters?
Before we talk about the different like of Neutral Density filters, let’s discuss the mount types first.
Just like any other filters, there are various ways to attach them to the lens. Below is a list of the few of the most popular options.
- Slide-In. The slide-in version of the Neutral Density filter requires an adapter or filter holder. This screws on to the front of your lens, and once attached, you can slide the glass into it.
- Screw-On. The screw-on version allows you to screw it on to the front of the camera lens.
- Drop-In. There are types of ND filters that sit in your camera body, just in front of your mirror. These are preferable, as they do not refract light as the others could.
All these mount types have their pros and cons. Slide-ins allow you to use the same size of filters on almost any kind of lens. But they’re bulky and aren’t always the best choice if you move around a lot.
Screw-ons are the most secure option, especially if you move around a lot when shooting. But you’ll need the proper size of filters to fit lenses with different diameters.
Drop-in filters are both secure and let you use one size of filter for any lens. But they can be quite expensive.
The two main types of neutral density filters we’ll talk about below may have any of the mounts we mentioned. So it’s up to you to weigh the advantages of each option and figure out which you like the best.
Neutral Density Filter Kits
Most neutral density filters come in kits.
On average, a kit has three to 5 filters with varying ND numbers. Each neutral density filter has a different rating. It starts from ND2 to ND8 or ND2 to ND64 or more.
What makes the neutral density filter kit useful is that you can combine filters to achieve the ND number you desire.
So let’s say you need an ND10 filter, but your highest option only goes up to ND8. What do you do? You can easily combine screw on an ND2 on the ND8 already on the lens, and you got yourself an ND10 neutral density filter!
Variable ND Filters
These two polarizers allow you to control different intensities of light coming through the camera. In other words, using a variable neutral density filter means you don’t need ten separate filters anymore.
All you have to do is twist the filter ND to offset the polarisation. When polarized at a 90-degree angle, the filter doesn’t let in any light. At 0 degrees, it lets in 100% light.
A variable filter works incredibly well. But it can also be quite expensive. Furthermore, you should be aware that it can introduce artifacts into the out of focus areas.
In most cases, you’re better off buying a kit of several neutral density filters. They not only lessen the chances of projecting artifacts, but they’re also cheaper.
Graduated ND Filters
A graduated ND filter is slightly different from a regular ND filter. Only a part of it has an ND coating while the other half doesn’t have any at all.
You won’t see any difference in the lower half of the filter. But the f-stop reduction gradually gets higher as you go up. The highest ND number of a variable neutral density filter is usually around two-thirds of the way up.
A graduated ND filter is for darkening a specific part of the image, not the whole scene. Photographers use them mostly for skies, especially since it can be 3+stops lighter than the horizon.
The purpose of the gradations in the filter is to make the transition from ground to sky a lot smoother. Otherwise, the separation line between the light and darkness would be too visible.
You can rotate these graduated filters if the lightest element is in the bottom half of the frame.
Likewise, if only the top third of the image is too bright, you can move the filters up or down to compensate. They come in the same strengths as the ND filters.
DIY Neutral Density Filters
Welder’s glass gives you ten stops reduction in light. However, using it will require you to do a lot of colour management in post-production. If you are interested, read this article here on how to process the final image.
What Is the Best Neutral Density Filter?
At ExpertPhotography, 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 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. It’s what I decided to use on our How to Use an ND Filter to Remove People from Long Exposure Shots article.
From my experience, these filters may not be strong enough on their own. And stacking them isn’t a great idea. They are plastic and will give your images a vignette, a coloured tint, and a higher possibility of refracted light.
That’s why I went with Lee’s Big Stopper later. It’s has a 10-stop reduction in light which is quite impressive. It won’t be enough for a solar eclipse (you’ll need two), but it will help in your landscape or street photography.
On a serious note, these filters aren’t cheap. But as they say, you get what you pay for. So if you’re going to use them a lot, then there is no question – Lee Filters are the way to go.
What Other Equipment Will You Need?
The first accessory you will need when using these filters is a tripod. You’ll need it to stabilise your shots especially if you’re doing long exposures.
A cable release or remote trigger is also essential because it doesn’t require you to touch the camera physically. Pressing the trigger remotely reduces the amount of camera shake and blurriness in your image.
And finally, you’ll need a lens cleaning cloth. You’ll be touching and changing out all the time. So it’s essential that you have something to wipe off the smudges on the lens.
Common Problems When Using ND Filters
I found several issues using ND filters. After my experience, 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 blurry final image.
Do not try stacking the filters if you have a cheap set. 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. But if your kit is made of plastic, the result isn’t going to be fantastic. It will cause light refraction, where the light entering will bounce between the two pieces of glass, showing you dust and light spots.
Furthermore, 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 challenging to remove.
We have a great guide to camera lens filters you can check here.
You’d be surprised how digital cameras tend to overexpose images even in normal lighting conditions. No matter what type of photography you’re into, you need to invest in ND filters. Always bring them in your camera bag. You’ll end up needing them more than you think.
To master long exposure photography, don’t miss out on our course – Infinite Exposures!