Let's face it...
There's a ton of neutral density filters out there.
And I'm not just talking about filters from different manufacturers, either.
There's all sorts of ND filters with varying strengths that give you much more power to create epic photos.
The question is, which ND filter is best suited for what task?
That's where this guide comes in.
Let's have a look at three popular ND filters - a 3-stop, a 6-stop, and a 10-stop - and what you can do with each.
3-Stop ND Filters
Best for: Portraits, Weddings, and Sunsets
ND filters are available in a variety of strengths, from just 1-stop to well beyond 10-stops.
That means that a 3-stop ND filter is on the lower end of the light-stopping spectrum.
A 3-stop ND filter has wide applicability because of this...
You can use one for outdoor portraits in which you want to open the aperture nice and wide to get a shallow depth of field.
You can also use it for wedding photography when you want to keep the ISO as low as possible to get nicely saturated, sharp photos.
Yet another application is for landscape photography and shooting sunsets.
A 3-stop ND filter can actually get you better results at sunset because the exposure time is half of that you'd have with a 6-stop filter.
By cutting the exposure time in half, you can minimize noise from the sensor, especially in areas of shadow in the scene.
Of course, you can always use a 3-stop ND to mimic a 6-stop ND, too.
For example, if with a 6-stop ND at ISO 100 you have an exposure time of four minutes, you can use a 3-stop ND at ISO 50 to get roughly the same exposure time.
That means that the 3-stop filter is a versatile addition to your collection of lenses, not just because of the wide range of subject matter you can photograph, but because you can manipulate its performance to mimic a stronger filter as well.
6-Stop ND Filters
Best for: Landscapes
Hands down, if you're a landscape photography enthusiast, a 6-stop ND filter is the one for you. In fact, if you buy only one ND filter and you primarily shoot landscapes, get one of these!
A 6-stop ND filter gives you the capability of getting gorgeous long exposures of moving water, passing clouds, and sunrises and sunsets.
With exposures in the two-minute to four-minute range, a 6-stop ND filter is ideal for situations in which you're shooting with a low ISO and a small aperture.
For example, if you're in the mountains at sunset and want to capture foreground interest in addition to the detail in the sky, you can set your aperture to f/16 or so, put the ISO at 100, frame the shot, add your 6-stop filter, and get a gorgeous capture of the scene before you.
And, as was mentioned earlier with the 3-stop filter, you can always halve your ISO to double the exposure time you can get with your 6-stop filter. Again, versatility is key!
You can also stack a 3-stop filter on top of a 6-stop filter to get 9 full stops of power. That will get you into the realm of shooting long exposures even on bright, sunny days.
But it would be a misnomer to say that a 6-stop ND filter is only for landscapes...
Hit the streets in the city with your 6-stop ND, and you can get exposures long enough to eliminate people from the shot while showing off the vibrant lights of the city as cars pass by and the clouds pass by overhead.
10-Stop ND Filters
Best for: Daytime long exposures
If your passion is daytime long exposures, like capturing urban environments, creating black and white images, or making abstract images, a 10-stop ND filter is for you.
A 10-stop ND filter can get you double the exposure time of a 6-stop, making it ideal for highly dramatic scenes like the one seen above.
For example, if you shoot at f/11 and ISO 100 with a 6-stop ND, you'll have an exposure time of around two minutes to four minutes.
However, with the same exposure settings and a 10-stop ND, you're looking at exposure times beyond eight minutes.
The effect of a 10-stop ND is especially useful during broad daylight when the sun's rays are overhead (or relatively close to overhead) and the light is flat.
For this reason, a 10-stop ND filter is a poor choice for sunrise and sunset shots, thus the reasoning for using a 3-stop or 6-stop ND filters for that purpose.
Other Factors to Consider
The subject matter you photograph isn't the only factor when choosing an ND filter.
Also think about your gear.
If your camera's minimum ISO value is 100 and you're a wedding or portrait photographer, get a 6-stop ND for more light-stopping power.
However, if your camera has a minimum ISO of 50, get a 3-stop ND.
Something else to think about is how versatile you need your setup to be.
For example, if you mostly shoot landscapes, a 6-stop ND is the best choice.
But let's assume that you occasionally want to shoot a daytime long exposure, too.
Rather than investing in a 10-stop ND filter, you might opt instead to get a 3-stop filter that you can stack on top of the 6-stop filter for virtually the same effect as a single 10-stop ND.
Of course, there are other filter options too, ranging from 1-stop to 10-stops, so you can mix and match as you see fit.
There's even ND filter kits that include three ND filters of varying strengths to give you greater versatility.
ND filters have a reputation for being a landscape photographer's best friend, and with good reason.
But as I've explained here, they're also great for portraits, weddings, and exploring the urban jungle.