Before you go all PC on me, know that I mean it. Used the right way, a photograph with the “right” neutral density filter makes me quiver. It goes beyond a photograph, it’s actually a time lapse event all in one frame. It’s arrested sensations frozen in megapixels, oogled by many or just a few. Yes, you could say that I kind of like long exposures but that’s an understatement, I really love crafting images which compress time.
There’s 3 basic types of Neutral Density (ND) filters and you need to know the difference between them, so you can use them properly….
The Subtle Differences between ND Filters
A standard ND filter uniformly cuts the amount of light entering the lens across the entire image area. It’s used for overall brightness reduction to use larger apertures, for portraits on a sunny day for example. An ND filter can also compress motion by increasing the amount of time it takes to expose an image at a particular F stop. If you were able to take a photograph on a cloudy day of rocks and water at F22 without an ND filter, it might just require a 1/8 second and render the wave movement into a soft cotton look using your ND filter to lengthen the time, from 1/8 to a 1/2 or a full second. It will change your image dramatically, yet leave the sky exposed properly.
A graduated ND filter screws on to the front element of your lens and allows you to decrease light in a portion of your image. Most people use this for landscape photography, where exposing for the foreground would over expose the sky. When using, you need to place the line of gradation on the horizon.
This is an example of what you get when you expose for the beautiful countryside but not the sky.
Using a graduated ND filter to cut the brightness in the sky, this is what you would get:
This is exactly a 2 stop difference in the sky, it’s obvious you would want the depth, the detail and the rich colors of the second exposure, right?
Once you start using a graduated filter like this one, you can start to see things and know what the filter will do. You need to think at first since your eye can see a vast range of contrast values but the camera sensor can only see a small fraction of what the eye can see. Soon you will intuitively know what the finished image will look like if you use this filter.
In my previous blog post, “Finally, a Beginner’s Guide to HDR” I cover how to use multiple exposures and blend them together to get the same effect as a Split ND filter. So what is the advantage of using one? There are two advantages; It allows for a single exposure and that means less noise and less movement in the frame. HDR captures 3 unique time slices, there may have been variances between those, which we count on the HDR software to resolve. It generally does but there’s a slight loss of sharpness and increased grain or noise. So the ideal solution for an image like the one above is actually the split ND filter.
Using Lightroom to “fix” an image with an overexposed sky is possible but results will vary. By using the “graduated ND” tool in the Develop module, you can generally correct this flaw as long as the sky is not completely white. It’s great to recover some of your older “mistakes” but it’s no substitute for a tool actually designed to handle this exact problem. I am sure Photoshop can be used as well.
The Variable Neutral Density Filter
The variable neutral density filter is the most versatile of all. But it is also a very complex piece of optical technology. Older/cheaper versions create “banding” on the finished image, “stripes” would appear at certain angles. This type of filter is absolute magic when used properly and the good news is that it’s very easy to use. It’s range is limited to about 6 stops. The downside of using a variable ND filter is using a lens hood that isn’t circular (as with many extreme wide angle lenses) is not possible. Circular lens hoods are fine and encouraged.
To me, the absolute top-of-the-line ND filter is made my a company called Lightcraft. I have this product because I think it’s worth the money. The Lightcraft Fader ND has been my favorite for some time, allowing me to capture the images on this blog and in on my website which would have been more difficult with other products. It’s about $200 and worth every penny.
In this exposure, I used it for 5 seconds, which was the length of an entire wave cycle. The wave was so powerful the ice itself, which is the size of a small car, was moving from the force of the water. Yet this technique allows for a softening of almost all the water movement to a still, almost dream-like state.
The variable ND filter is the most expensive of them all. It’s also the one filter where you can’t skimp with a low priced version, it’s not worth it, you won’t like the results. It has other applications besides water, because I had these files from my own trips, I used them for illustration here.
Black Glass ND filters are typically 9 or 10 stop fixed “extreme” ND filters and produce some very interesting results. They are considered the most dense, allowing in 1/1000 of the light you are shooting, they are what I would call special purpose accessories and have a place in the ND world.
Uses for ND Filters
- Portrait photographers will love this tool, since it allows you to shoot with the exact aperture you want, still maintaining a low ISO and not worrying about too much light.
- As an idea, you can use a split ND filter to shoot portraits where one side of a person is darker than the other, orienting the filter vertically, you could say you are showing both his good side and his “dark” side.
- Architectural photographers have used ND filters to achieve a particularly pleasing effect; clouds softly streaking behind a stark, sharply lit sky scraper. The work of a modern day master of the extreme ND filter: http://www.redbubble.com/people/jtjintjelaar – His work is amazing, just enjoy!
- Erasing cars is another favorite use for ND filters, since cars move on the highway so fast that in light traffic you can seemingly capture empty cityscapes. Try experimenting with this, it’s a blast.
- Recently I have been experimenting with trees and ND filters. Here is where you can break the rules about wind. On windy days, use your ND filter to photograph trees in the forest. With a lot of wind, the trunks are visible and the tree tops fade. Depending on the amount of time the shutter is open (using the “variable” aspect of the Variable ND filter) I have been getting some interesting results.
Some Cautions When Using ND Filters
- Unlike the suggestion above regarding wind as a creative tool, avoid wind when your shutter is open for a long time if you are shooting things that shouldn’t move. Even if your subject won’t move, in brisk wind, your camera will shake. Particularly true with architecture since sharp lines are important. Just go home, it’s not worth even setting up.
- Avoid small F stops. If you are using a Variable ND filter then you can typically afford to back down your F stop to F8 or F11, since beyond that you may be subject to diffraction, which is when light scatters and bounces off the edges of the aperture blades cause the image to soften, which is generally not desirable. For a more in-depth discussion of diffraction go here.
- Don’t skimp on cheap glass. I know from having already done that, it’s not worth it. Buy the best or wait until you can.
- Polarizers are, in a sense, doing something similar to a variable neutral density filter but “polarize” (accept light in one particular angle and block the rest to some degree) and block reflection off surfaces you are photographing. They are NOT ND filters. If you are OK with the effect, this is a good substitute and are usually good for cutting light by about two stops.
In summary, the ND filter is an awesome tool that can blow your creative photography out of control! It’s one of those things that is much more than you think it is. Go stop time for a little while, send me what you do, I would love to see it!
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