Recommended ND Filters and ND Filter Strengths
In this article, I look at the common problem of which Neutral Density filters to buy for landscape photography. Two questions crop up with regularity when it comes to choosing Neutral Density filters, or ND filters to use the common abbreviation:
- Which ND filters would you recommend?
- What strength of ND filter should I buy?
In this tutorial, I answer both questions and give you enough information to be able to make informed decisions in the future.
Why Use ND Filters?
ND filters or Neutral Density filters have one purpose; they slow the shutter speed of the cameras. They are very popular with Landscape Photographers as they allow us to blur moving subjects whilst keeping stationary subjects perfectly sharp. You can see an example of this in the sunrise scene below.
Notice the distant mountains and foreground rocks are sharp but the waves on the sea are smooth. I created the effect by keeping the camera still on a tripod and using a Neutral Density filter to extend the exposure. It’s the extended shutter speed of 10 seconds that causes the motion of the waves to blur out.
What Are ND Filters?
The ND filter is a dark piece of glass or optical resin which is placed over the end of the lens. Because it’s dark, it reduces the level of light reaching the camera’s sensor. This causes the camera’s shutter to open for longer as it tries to produce a good exposure.
The filters come in two types; screw in and square slot in.
The screw in filters’ screw onto the end of the camera lens or onto an existing filter screw in filter attached to the lens. They have the advantage of reducing the chance of light leaking around the edges of the filter when using very strong filters. The disadvantage is they can quickly cause vignetting with wide-angle lenses if you need to stack multiple filters together.
The option preferred by most landscape photographers is the square slot in filter design. Here a filter holder attaches to the end of the lens using an adapter ring. The filters then slot into the holder. Most filter holders are much wider than the lens which avoids vignetting, even when you combine multiple filters on a wide-angle lens.
Filter manufacturers use either optical resin or glass for the filters. Optical resin tends to scratch easily, and the surface of the filters can become covered with micro scratches. These are very hard to see but when you try to shoot towards the sun, they produce lens flare. Glass filters tend to resist scratching but can shatter if you drop them. This was one of the reasons I originally switched to Kase and recommend their camera filters. They don’t break even when dropped. I know, I’ve dropped mine on a tarmac road a couple of times now.
Be Sure Your Filters Are Neutral
ND filters derive their name from the fact they are neutral. This means they don’t affect the colour of the image when you use them. This is a common problem with cheaper filters which tend to introduce a colour cast that can ruin an otherwise great shot. You need to buy quality to avoid this problem and quality tends to cost more.
A further problem that I have experienced with resin filters is that they can discolour over time. Even when a filter starts off neutral, it can become discoloured as either the dye in the filter either isn’t stable or pollution from the air can enter the edges of the filter. Some of my old resin filters (not the Kase Wolverine) have turned an orange/brown colour.
The neutrality of filters can also become a problem as the strength of the filters increases. A common problem found with stronger filters such as 10 stop ND filters is that some cause a strong colour cast. In the past, I’ve owned 10 stop filters that create both brown and blue colour casts. This isn’t too much of a problem if you want to convert your image to black and white, but if you want to shoot in colour it can be very difficult to correct.
The best advice is to always by good quality ND filters and I would again recommend Kase Wolverine filters as being very neutral.
Understanding ND Filter Strengths
We measure the strength of a Neutral Density filter by the light reduction they produce, which we measure in stops. Take the example of the weakest ND filter which will remove 1 stop of light. This causes the shutter speed of the camera to double, assuming nothing else changes. We then rate this filter as an ND2 filter because it doubles the shutter speed, the 2 indicating how much longer the shutter speed is.
If we have a two-stop filter it would remove two stops of light. This would cause the shutter speed to double and then double again. This is, therefore, an ND4 filter, the 4 coming from 2 x 2 or a shutter speed that’s four times longer than without the filter.
Taking a more extreme example, a six-stop Neutral Density filter would slow the shutter speed by 6 stops or 2 x 2 x 2 x 2 x 2 x 2 x 2 = 64. This is, therefore, an ND64 filter.
What Strength of ND Filter Should I Buy?
Let’s now address the big question of what strength of filter to buy. The answer to this question does depend on your photography and what you’re trying to achieve. Remember, the purpose of the ND filter is to slow the cameras shutter speed. How much you want to slow the shutter speed is the important point and why.
There are probably two main reasons why a photographer might want to use an ND filter:
- To reduce the chance of overexposing an image.
- To create artistic effects.
In the first case, the exposure might become a problem when shooting outdoors in very bright light. In some circumstances, this might require a shutter speed that’s faster than the photographer wants to use or even faster than the camera can produce. Using one of the lesser strength Neutral Density filters in the range of 1 to 3 stops would solve this problem.
In the second case, we might need to use a much stronger ND filter depending on the time of day and strength of the sun. If you’re likely to be shooting at different times of the day with different lighting levels you’re probably going to need more than one ND filter. Let’s look at a couple of examples.
Shooting Bright Light
If you’re shooting in bright light and you need to slow the shutter speed because it’s beyond the camera’s limits, the best strengths are likely to be ND2, ND4 and ND8 (1, 2 or 3 stop) filters. If you only have the budget to buy one of these ND filters, the ND8 strength is likely to be more versatile. If you find using this filter slows the shutter a little too much you could always open the aperture and/or increase the ISO setting.
When shooting in bright light and you want to capture blurred movement, the ND64 (6 stop) filter is likely to be the minimum strength you will need. You may, however, find the ND1000 (10 stop) ND filter offers greater flexibility for this type of work. The strongest Neutral Density filter in the Kase Wolverine line is the ND64000 (16 stop) but I wouldn’t recommend this as a first filter.
Shooting in Low Light
Another common situation is when shooting at dawn or sunset and you want to extend the shutter speed to capture movement. Sometimes it’s possible to achieve this using only the ISO and/or Aperture settings of the camera. If you find this isn’t enough you will probably find either the ND8 (3 stop) or ND64 (6 Stop) filters offer the required reduction in shutter speeds.
Recommend ND Filter Strengths
Assuming you are a landscape photographer who will be shooting in both bright and low light conditions as described above, the following advice might help.
If you only have the budget to purchase 1 filter, the ND64 (6 stop) is probably the best compromise. Also, consider pairing this ND filter with a polarising filter if you have one. The polarizer will typically reduce the light by around another 2 stops, giving an 8 stop reduction overall.
Where your budget allows you to purchase 2 Neutral Density filters, consider the ND8 (3 stop) and the ND64 (6 stop). You can combine these in a single holder to give 9 stops of reduction in light and if you add a polarizer, that’s around 11 stops. You will also find using the ND8 and ND64 filters individually or combined with a polarising filter offers a lot of flexibility. Whilst I also personally own ND1000 and ND64000 Neutral Density filters, it’s the ND8 and ND64 filters that I use most of the time. And if I need to reduce the weight of my equipment, I will take just the ND8, ND64 and polarising filters.
I hope you’ve found the recommended ND filters and advice over strengths helpful. If you have any questions, feel free to add them in the comments below. Alternatively, you can contact me using this form.
Read more about using camera filters for landscape photography.