How to Create LONG exposures with a Neutral Density Filter

Slowing down your shutter speed from the usual fractions of a second, to shutter speeds measured in whole seconds can add a real “wow” factor to your pictures. You can change the whole look of a scene to emphasize motion, or make it look calm and serene. Long shutter speeds do this by blurring water or grass, and by showing movement in clouds, among other effects. Using a long shutter speed can also cause people going through your frame to appear to be moving, or even to disappear from the picture entirely.

Getting your camera to use a shutter speed that is slow enough for these effects isn’t always possible though.

In times and places of bright light you will not be able to use a slow enough shutter speed without overexposing your picture, even when you use your smallest aperture (to let in as little light as possible) and use the camera’s lowest ISO setting (to make your camera require the maximum amount of light for an exposure).

So how to do you slow down the shutter speed further to get these effects?

The answer is the neutral density filter.

This filter is perhaps the most under-appreciated tool in photography. It will allow you to achieve all of these effects, and in this article I want to show you some tips for mastering it.

Selecting a Neutral Density Filter

The neutral density filter (or ND filter) is a simple device that is easy to use. It is a glass filter that screws onto the end of your lens (or drops in front) that uniformly restricts the amount of light allowed to pass through. When you attach it, the camera can only achieve a proper exposure by letting in more light – which usually means using a much longer shutter speed (exposure time).

A neutral density filter is often referred to as sunglasses for your camera, and that is a good way to think about it. If you don’t have one already, you’ll need to buy a neutral density filter. When purchasing one, here are some things to consider:

• Strength: ND filters come in a variety of strengths, which are measured in “stops” of light. If you don’t already have one, start with a 10-stop neutral density filter (6-stop is a good second choice). It is strong enough to create the effects you are looking for in almost any conditions. You can supplement it with milder filters later if you feel the need.
• Type: You can get a neutral density filter that either screws onto your lens, or you can get a Cokin-type rectangular filter, that attaches to the lens by means of a special mounting bracket. Although these filters work better if you anticipate stacking your filters (see below for more about that), I generally recommend the circular filters, as they are much easier to work with.
• Size: Assuming you are purchasing a circular filter, be sure you get the right size filter for your lens. The filter size will need to match the diameter of the front of your lens, which will usually be printed on the face of the lens (or on the back side of the lens cap). The lens diameter will be in millimeters, so do not confuse it with the focal length of your lens (which is also in millimeters).

  

• Quality: Remember that your image will pass through this filter, so you want to get a good quality filter that won’t degrade the image. It doesn’t make sense to spend all that money on high quality lenses only to place cheap glass in front of it.

Some things to keep in mind

In addition, when it comes to the strength of the neutral density filter, there are a few other things to keep in mind:

First, you can stack filters to increase their strength. In doing so, remember that a polarizer reduces the light that gets to your camera by 1.5-2 stops, so it can be used in conjunction with neutral density filters.

Second, you can also buy variable-strength neutral density filters, which allow you to adjust the strength by turning the filter. While I personally do not like these filters – the ones I have used were just two polarizers attached together and left streaks across my pictures – other photographers seem to have some success with them.

Note from Darlene: I actually have the ProMaster variable one and it’s quite good.

Again, I recommend you start with a 10-stop neutral density filter – that will be the one that I show you how to use in this article (but much of it will be applicable to ND filters of other strengths as well).

No matter which ND filter you choose, once you have it, you just screw the filter onto the front of your lens when you are ready to use it. You do not need to twist it to any particular position (unless you are using a variable-strength filter).

Once attached, assuming you bought the 10-stop filter, there will be 10 stops LESS light let into the camera. You will need to adjust your exposure accordingly, we’ll get to that shortly.

The 5 Steps to Master the Neutral Density Filter

Using the 10-stop ND filter can be a challenge. It is powerful medicine and its power leads to side-effects. The remainder of this article will walk you through its use and show you how to deal with those challenges in five steps.

Step 1: Focus the camera before attaching the 10-Stop ND Filter

10-stop ND filters are dark – really dark. They are so dark that most of the time your camera cannot see through them at all. When you look through the LCD, you will just see blackness. If you set the Live View on your LCD, sometimes you will see only black as well.

This means that your camera cannot focus on its own. So, to set your focus, you will just need to do it ahead of time. Before you put the filter on your camera, just set the focus as you normally would. If you use back-button focus, that’s all you need to do. If your focus is set by the shutter button, then you should switch your focus mode to manual focus after it’s set, (usually marked as MF on the side of your lens) so that your camera will not attempt to refocus when you press the shutter release button to take the picture. After you have set the focus, put the ND filter on the camera and take the shot without changing the focus.

Step 2: Set the Exposure Value before attaching the 10-Stop ND Filter

The darkness described above has another side-effect. Your camera’s internal light meter will often not work properly with a 10-stop ND filter attached to your lens. But don’t rush out to buy a separate light meter just yet! There are workarounds. Actually, this is an area where a good working knowledge of exposure will pay dividends.

Start by setting your exposure as you normally would, before attaching the ND filter to your lens. After the exposure is set, attach the filter. You know that this is a 10-stop ND filter, so you just have to remove 10 stops of light from your current exposure settings. Assuming that your camera makes adjustments at 1/3 stop increments (most do, and if you aren’t sure, this is a good time to dust off the camera manual and check) that means you have to dial back your exposure setting by 30 clicks. In other words, you have to remove 10 stops of light, and it takes 3 clicks to remove a stop of light, so you have to move 30 clicks.

In some cases, you can just lengthen your shutter speed by 30 clicks. If your shutter speed was 1/125 before you put the filter on your camera, then after moving 30 clicks, your shutter speed will be 8 seconds, which may be what you want. If it is, you are all set. If it is not, you will have to bring Aperture and ISO adjustments into the equation. In that case, use a smaller aperture, or reduced ISO, to slow the shutter speed down further (or vice versa). To keep it all straight just keep track of your clicks. As long as you decrease the exposure value by 30 clicks, your exposure should be spot on. But remember – in this era of digital photography a redo costs nothing, so if it isn’t quite right just make an adjustment, and try again.

Step 3: Using a Shutter Speed longer than 30 seconds

Most cameras only allow for shutter speeds as long as 30 seconds. If you add a 10-Stop ND filter to a relatively low light situation, you may need to use a shutter speed that is longer than that. There is a simple answer to this problem, which is to Bulb mode. In this mode the camera will expose pictures however long you want, infinite length. It is best to use a remote shutter release when setting the shutter speed. You can either click (and lock) the remote shutter release and set an external timer (like on your smartphone) to the shutter speed you want, or you can get a remote shutter release that acts as an intervalometer and times very long exposures for you.

You will often run into this problem if you are bracketing your photos. You can bracket your photos with a neutral density filter in the same way as without a neutral density filter. It just takes more time, due to the longer exposures. If you start with a shutter speed that is around 30 seconds, then the camera will not be able to create the overexposed image as part of that bracket. That is, the camera can not take an exposure any longer than 30 seconds, so the picture will not be overexposed the way you want. Again, the answer is just to take another picture using Bulb mode with the exposure longer than 30 seconds.

Step 4: Capture moving objects in the photo that you do not want blurred

Sometimes you will want to use a neutral density filter but there will something in your image that is moving, that you do not want to appear blurry. This happens to me a lot because I like to take pictures in harbors, and while I want the water to be blurred and the sky to show movement, at the same time I want the boats to be completely sharp. There is always a slight rocking and movement to the boats, so if you use a long shutter speed this will show up as blur in your photos. Even if you do not see the blur in your LCD, you will see it when you get back to your computer.

The way to deal with this is to take two pictures. First take a picture with the neutral density filter on your lens, and do not worry about the blur in the boat (or other moving object). Next, remove the filter and take a picture of the exact same thing. Be careful as you unscrew the filter from the lens, making sure not to move the camera at all, then reset your exposure and take the shot again. Now you will have two pictures that you can blend in Photoshop later. The first will have the water blurred and/or moving clouds you want. The second will have a sharp boat or other objects.

In fact, I typically use this technique anytime I am using the neutral density filter. There will often be little things that look sharper at faster shutter speeds and I can blend them in later.

Step 5: Fix any tint to your pictures created by the filter

Some neutral density filters add a slight color cast to your pictures. You can sometimes avoid this problem in the first place by buying a more expensive filter. When using a 10-stop neutral density filter, however, it seems almost inevitable that the filter will add a slight warm tone to the image. In any case, there is a pretty easy way to get rid of any color cast the filter may apply to your picture, it is available whether you use Lightroom, Photoshop, Photoshop Elements, or other software.

Typically a simple White Balance adjustment will remove the color cast. The best way to do it is to use the White Balance targeted adjustment tool, which looks like an eyedropper. It is located next to the White Balance sliders in the Basic panel of the Lightroom Develop Module. In Photoshop and Photoshop Elements, it is on the Adobe Camera Raw screen, on the top row of tools. Just click on the eyedropper, then click on a neutral color value in your picture. The best way to do it is find something that is white and click on that.

Usually, this simple click will remove the color cast (and set your White Balance at the same time). If it didn’t work the way you wanted, just click on a different point until it looks the way you want. In the unusual event that you cannot remove the cast in this way, just use the White Balance sliders to adjust the color manually.

Further use of Neutral Density Filters

This article has focused on using a 10-stop neutral density filter to achieve longer shutter speeds (long exposures). There are other uses that I would be remiss if I didn’t mention. The first is that you can also use a Neutral Density Filter if you want to use a larger aperture than you would otherwise be able to use because of the amount of available light. You might want to do that to get a shallow depth of field in the middle of the day. You might also want to do that to avoid the diffraction that the smallest aperture sizes cause.

Again, however, the primary use for a Neutral Density Filter is to dramatically slow down your shutter speeds. Used properly, the 10-stop ND filter will allow you to achieve effects that are not possible to add in post-processing. It will add a real “wow” factor to your photos especially when there is water, clouds, or moving lights involved. Try it the next time you see any of the following:

• Coastlines
• Waterfalls
• Rivers or creeks
• Moving clouds
• Tall grass and/or leaves
• Fountains
• Harbors
• People in your way

Good luck!