ND Filters 101: 8 Things You Need to Know

In Features by Mark Morris

Photographers LOVE jargon and fancy terms.  Virtually every photographer is a creative soul, looking for a way to express the way we see the world.  My guess is that about 98 percent of us are also a bit of a technology geek.  We photographers tend to like the technical side of our camera gear, and the “sciencey” side of capturing images.  Any time a photographer has a chance to toss around technical terms like “Neutral Density,” we love it!  The actual definition for the device really makes it a lot more simple to think of right away:

“a photographic or optical filter that absorbs light of all wavelengths to the same extent, causing overall dimming but no change in color.”

Waterfall with ND filter

Waterfall with ND filter

So what the filter companies are trying to do is to develop a piece of glass that will prevent a certain percentage of light from passing through your lens, and hit the sensor on your camera.  There are several different ‘sub-types' of Neutral Density filters (We'll call them ND filters from now on.)  The biggest problem

Variable ND Filters

These devices have a spinning part that twists or spins so that the filter covers a range of options.  It will prevent just a tiny bit of light, or it can be adjusted to prevent a lot of light.  On the surface this looks like it might be a great option, because it's one filter to rule them all.  There's only one problem… they tend to REALLY spoil the look of the images that are taken with them.  That's kind of a big deal.  The way that they work is similar to two circular polarizing filters connected together.  There are two big problems: 1) they tend to have a very strong color-cast, and 2) there is often a very discernible “X” shape superimposed on the image due to the way the two moving parts align.

Graduated ND Filters

These filters are meant to adjust the amount of light in one portion of your image, while leaving the other portion of your image unchanged.  The biggest use case that comes to mind for this is a super-bright sky.  If you are shooting a beautiful landscape, but the sky is extremely bright, you can put a Neutral density filter on your lens, to prevent some of that light on the top half of your image from over-exposing.

This is really a big left-over from the film camera/darkroom days.  I honestly believe that if the optical companies were inventing their products in 2016, given all of the tools that photographers have at their command in a computer, they probably wouldn't even invent these things.  Here's why: Other than shooting the ocean horizon, how often do you have a perfectly straight horizon line, with NOTHING jutting up above it (i.e. trees, mountains, a building… you get the idea.)  So a graduated filter will taper from heavy blockage of light to no blockage of light, and that horizon line will effect your image in a straight line.  This filtering can be done within a post-processing program, and you can utilize brushes that will allow you to pull down the exposure on the sky, without effecting a mountain, or a person, or any other object that might stick up above the horizon line.

While graduated ND filters certainly have a lot to offer in terms of creativity, my personal opinion is that the limitations I just described make them fairly undesirable.  Just to be completely forthcoming as an author – I have never owned a graduated ND filter.  I have never used one.  I am forming my opinion based on a perception and an expectation, and from what I have heard from other photographers on the topic.

Neutral Density Filters

Good old-fashioned Neutral Density Filters (not variable, nor graduated), manipulate the amount of light coming through the lens.  This amount of light limiting is evaluated in ‘stops.'   If you are not familiar with “stopping down” or what an “f-stop” is, I will refer you to the “Explainer-In-Chief”, Jeff Harmon.  His Photo Taco episode does a magnificent job of explaining what an f-stop is.  You can purchase various ND filters to effect the light through-put of your lens by 1 stop, all the way up to 10-stops.  Each “stop” is an exponential amount of light less than the stop before it, so by the time you get up to a 10-stop filter, you are basically looking at a filter that appears to be black glass.

So the next logical question is: ‘You have just explained that this can be done in Lightroom or Photoshop, so why do I need to spend money on an ND filter?”  I think there are some HUGE reasons why.  Every aspect that enters your consciousness when setting up your camera for a photograph will benefit from having ND filters at your disposal.  Some of the most standard scenarios are:

1. Motion Blur

This is probably the most common use that everyone has seen for an ND filter.  When you are photographing waterfalls, or the ocean, or a stream, and you want that blurred water effect in your image, you need a fairly long shutter speed.  Say for example you want a 5 second exposure.  On a bright day, with your ISO all the way down to 100, and the lens as closed down (highest number setting) as you are interested in using, you may not be anywhere close to a 5 second exposure.  You might be at a 1/60th of a second exposure, with no hope of getting a nice long exposure, without over-exposing the image.  Blocking out a lot of the light from the lens will let you achieve this.

2. Shooting for a Particular Depth-Of-Field

Let's say you have a shot where you want to create a lot of bokeh.  You want your lens to be wide open, but that's letting too much light through.  If your ISO is already as low as it can go, you are basically limited to how open you can set your lens.  BUT… if you can limit the light another way (the ND filter), then you can keep that depth of field that you were hoping for in your composition.

3. Keeping your lens open enough to avoid diffraction

Ok – time for another reference to the Explainer-In-Chief.  Jeff Harmon has JUST done a fantastic job of explaining diffraction.  Rather than go into a long explanation here, I'll provide a link to his Photo Taco episode on the subject.  But – for a very short version of the explanation: light behaves oddly when our lenses are closed down too small.  The same physics that create the really cool starburst effect that we all know and love around f/16 or f/18 also has some very unwanted effects as well.  This all has something to do with light waves bending as they go around the corner of a surface… and for me, that's all the information I need about it.  But if you are really into the complete understanding of the world in which you live, you may want to stop over to the Photo Taco Podcast group on Facebook!  I assume the discussion there involves physicists.  If not, at least it involves people who have had a great physics class, or physics teacher.  I, on the other hand, have not!   Suffice it to say, for a photographer, you probably don't want to have diffraction issues in a photo.  That means you don't want to close down any farther than maybe f/16 or f/18 on a lens, even if the lens itself will let you close down to f/32.  Even the most expensive lenses have this problem, because it's a matter of the physical world we live in.  It's inescapable with our current technology.

4. Dealing with Flash

We have a detailed article coming out on this topic very soon, but here's the mini version:  If you are outside on a really bright day, and let's say you want to use a wide open lens for a shallow Depth Of Field, but you need fill flash to handle some shadows… you have a HECK of a lot of light to contend with.  The flash sync speed is probably something around 1/250, and in order to make that work with a bright day AND fill flash, you are looking at an f-stop that will need to be very closed down.  If you want to avoid closing down the aperture, you have to block out some light in some other way.  That is where the ND filter comes in.  If you have a good set of options in your bag for stopping light with an ND filter, you can still use the 1.4, 1.8, 2.8 aperture, and keep the shutter speed slow enough to sync to your flash.

5. Making People Disappear

We have all wanted this super power at some point in our lives!

Let's say we are photographing a busy town center.  People are hustling and bustling through the scene.  If you can extend your photo long enough, the people that are passing through the field of your camera as pedestrians will not even show up in your photograph.  This is a really creative and exciting technique to explore in busy urban areas.  It also allows you to photograph architecture or landscapes where people are present, but effectively take them out of the equation with your camera, instead of with “content-aware fill.”

6. Unleashing Creativity

I feel that use of ND filters and long-exposure photography in general are superb ways to unleash your own creativity in your photography.  Every photographer goes through a progression.  At some point, one is simply trying to figure out how to set the aperture, shutter-speed and ISO to get a proper exposure.  That would probably not be the most ideal time to start experimenting with various ND filters.  However, when you have a very solid grasp of the fundamentals of shooting, starting to explore with the use of filters in your work can be extremely motivating!  Having a new piece of gear is always a fun way to kick start your photographic creative juices.  Sometimes that new piece of gear is not going to be a new $2,000 L lens.  Sometimes it can be something far less expensive, that gives you a completely new perspective on the craft and art of photography.

7. Which Ones Should I Buy?

This is a superb question!!!  In fact, I am currently preparing a large-scale review of a wide array of ND filters.  From June 20th to July 7th I will be testing and evaluating filters from some of the greatest manufacturers in the industry.  My goal is to bring you some completely unprocessed images shot with each of the different filters in order to let you evaluate the “look” of each one.  I am still receiving final confirmation and shipments from a number of the manufacturers, but this review should include all of the following:

B+W

Breakthrough Photography

Formatt-Hitech

Heliopan

Lee Filter System

Manfrotto Filters

Promaster Filters

Tiffen Filters

Vü Filters

For those of you who are familiar with all of the ‘big names' in filters, you will notice just a couple that are missing here.  I am actually still working with the representatives from a couple of the other major manufacturers, and it sounds like the list above will be growing by a few more with some late arrivals.

8. What Price Points Will Be Covered?

This survey of filters will cover the gamut in terms of price points!  My objective is to pick a “best” option for several categories:

  • budget/beginner
  • mid-line/hobbyist
  • upper end/advanced hobbyist
  • Top Dollar/Professional

Filters will be covered that cost less than $100, and it will progress all the way to professional filter systems that cost many hundreds of dollars.  The goal is to provide you with sample photos of the same basic set-up, shot with TONS of different filters, so you can see for yourself how they perform against each other.

But Wait, There's More!

Some of the manufacturers have provided copies of their filters to be distributed as part of a give-away to Improve Photography readers.  There are a couple of places that you can follow me in order to receive notification of those give-aways.  Instagram and Facebook are the best two places.  I know that there aren't too many images in this particular article, but I will be sharing TONS of long-exposure photos in the coming weeks.  I'll make sure to specify exactly which filters were used in the creation of each image, as well as the exposure length, camera/lens settings, etc.  I look forward to sharing these photos out as they are created, and most of all to sharing out the results of a ton of real-world testing that could save each of you hundreds or even thousands of dollars in experimenting with the many different options out there.

 


About the Author

Mark Morris

Mark is a part-time professional photographer living in Suburban Philadelphia. He has a thriving wedding & portrait photography business, and works extensively with performing artists; primarily musicians. Commercially he has worked with Disney, Steinway & Sons, and numerous lifestyle and fashion websites. He lives in North Wales, PA with his amazing wife Alexis, and their sassy bulldog, Lily.