Neutral Density filters have one purpose, and one purpose only. That is to reduce the amount of light hitting the lens. The result of this is three-fold. You can extend your shutter speed to allow the camera to gather more light, open your aperture to let more light in, or increase your ISO for more light sensitivity.
I don’t recommend the ISO adjustment, but I do recommend the other two. And each has their areas of uselessness.
Before we dig into those approaches, let’s talk about the differences between the various neutral density filter options.
There are two main types of neutral density filters, and then three other variations on those types.
Screw On Filters
First up are the screw on filters. These are like your typical UV or Polarizer filter, where you physically screw the neutral density filter on the front of your lens.
These are great because they’re inexpensive, for the most part, and standard when compared to your other filters. If you go with the screw on style filter then I recommend picking up whatever filter fits your largest lens. For example, a 77mm is relatively common for lenses. Then, pick up step up rings for your smaller lenses. For example. if you have a lens that accepts 55mm filters, then purchase a step up ring that converts 55mm to 77mm. These are usually only a few dollars.
Slot Style Filters
The other type of filters is what I like to call Slot Style Filters. These are square or rectangular, depending on the filter, and slide into a bracket that you have mounted on your lens. Like the screw on style filters, the bracket for slot style filters requires screwing on the front of lenses. But the beauty of the bracket, is that it can be clamped on to any lens at any point as long as the adapter ring exists.
The two core brands known for their slot style systems are Lee Filters and Formatt Hitech.
As mentioned, there are multiple variations of neutral density filters. Not all brands make the variations in both types of filters. However, many do – so be sure to do your research before jumping into a filter setup.
First up are the solid neutral density filters. These reduce the light evenly across the entire frame. Every company who makes neutral density filters makes the solid variation.
Next are graduated neutral density filters. These use a graduated spectrum from clear to dense. Within graduated ND filters are both soft and hard graduations. The difference being how quickly the filter goes from clear to dense, or how slow and soft it does.
Most of the time graduated neutral density filters are found as slot style filters. However, some companies have decided to take on the challenge of creating screw on style graduated neutral density filters that work similarly to a polarizer. I use the slot style, so I cannot say how effective the screw on style works in this case.
Going along with graduated ND filters are reverse graduated ND filters. These come in a variety of styles including clear to dense to clear again.
The last is the variable neutral density filter. This is very much like a polarizer mixed with a solid neutral density filter. Typically these filters range from 1 to 8 stops of light reduction. You first screw on the filter, and then as you turn the filter, you are effectively increasing the density. Unfortunately these can be known to have poor quality and in some cases present a strange shadowy X on top of your photo.
My preferred neutral density system are from Formatt Hitech in their Firecrest line of filters. They’re slightly on the higher end of the price spectrum. If you cannot afford them, then I’d recommend checking out Lee Filters, B+W or Hoya.
Neutral Density Filter Techniques
Extend the Shutter Speed
The most obvious case for using neutral density filters are for long exposures. These can be of moving objects, water, light painting, stars, etc. Here’s a typical scenario of how a long exposure would play out.
You are staring at a beautiful waterfall that you want to photograph. But the sun is way too high in the sky to achieve smooth water due to the shutter speed. Your camera is metering at f/8 with a shutter speed of 1/1000. That’s fast. Too fast.
So you attach a ten stop neutral density filter, either screw on style or a slot in style. Using a bit of math, or a neutral density calculator, you determine that with a ten stop ND filter your shutter speed will extend to 1 second of time. That is more than enough to get smooth water from your average waterfall.
Opening the Aperture
The other side of the coin is the aperture component. The perfect example is when you are at the beach and want a portrait with a shallow depth of field, like at f/2.8. Usually that’s hard to do because of the extremely bright sun,.
But when you throw on a neutral density filter, you are reducing the amount of light passing through it. So opening the aperture will bring back the light you list, and in turn, give you that shallow depth of field.
It’s a win-win if that’s your goal.
There you have it. Now you know what neutral density filters are, the various types of filters as well as two useful situations where they would come in handy.
To get a better understanding of neutral density filters, please check out my ebook, Time is on Your Side: Exploring Long Exposure Photography.
Finally, if you do plan on doing long exposure photography, be sure to pick up a cable release or a Triggertrap. You will thank me later.