Neutral Density Filters and Graduated ND Filters

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Neutral Density Filter of a waterfall

Neutral Density Filters, or ND filters, may not initially seem very interesting to amateur photographers because all they do is reduce light, but they can be an important tool for professionals. For amateur photographers, understanding light can be a bit of a challenge. What amateurs don’t realize is that it’s all about control of light and sometimes you want more and sometimes less.

They are referred to as neutral because they don’t affect the color of light passing through the filter. You can think of them as sunglasses for your camera. Just as you would use sunglasses to reduce the light to your eyes, photographers use ND filters to reduce the light to the sensor (film).

Understanding light becomes easier when you get the hang of the shutter, aperture, f/stops, and how the photographic triangle works.

Reducing light

Ok, so you may be wondering why you should have a filter that reduces light when you’re already able to reduce with the camera itself. If all you were looking for is having the correct exposure, then yes the camera can take care of it for you in most cases, but Neutral Density Filters give you ability not only to have correct exposures but also to have the control over creative exposures.

Neutral Density filters give the photographer the ability to control light separate from using the Aperture or Shutter

When should I use Neutral Density Filters?

Slow shutter speeds and longer exposures

Probably the most common use for ND filters is for photographing waterfalls, rivers, and streams. In order to capture the look of smooth flowing milky water you need to have your shutter stay open long enough. This usually isn’t possible on sunny or even overcast days. Using a neutral density filter can decrease the amount of light by 1, 2, 3 or more stops allowing for a slow shutter speed. The two images below shows a waterfall taken at 1/125th (no filter) and at 1/4th a second (ND64 or ND 1.8).

No Neutral Density filter used

Shutter speed 1/125th - No ND Filter being used

Neutral Density Filters used

Shutter speed 1/4th - Neutral Density Filter equivalent of 1.2 being used

I’ve decreased the amount of light passing through the lens by 6 stops. You can easily see the difference in how the water looks in the two photos.

Quick note: I didn’t actually use a ND64 filter, but instead I used a ND2, ND4, and ND8 filter combined. Together this gives me the same effect as a ND64 filter. The chart below shows the strength of the most common ND filters. Notice that if you combine the filter Optical Density of those 3 filters (0.3, 0.6, 0.9) that you get 1.8 which is the same as the ND64. This saves you from having to buy additional filters. You can buy stronger ones, but there use may be limited for the average photographer.

Filter number Filter Optical Density F/Stop Reduction % Transmittance
ND2 0.3 1 50%
ND4 0.6 2 25%
ND8 0.9 3 12.5%
ND16 1.2 4 6.25%
ND32 1.5 5 3.125%
ND64 1.8 6 1.563%

Wide Apertures and shallower depth-of-fields

Just as neutral density filters allow you to slow your shutter down it also gives you the ability to open your aperture wider and get a shallower depth-of-field. Maybe you want to take a portrait shot on a bright sunny day and are limited by the maximum shutter speed you can use. You want to shoot at an aperture of f/2.8, but your aperture can only open to f/11 without overexposing the shot. In this case you would need to reduce the light by 4 stops. By using a ND16 or ND 1.2 filter (or combining the 0.9 and 0.3 that equals 1.2) you can get the effect you want.

Making people vanish, without magic

How many times have you taken a photo of a famous landmark and hated the fact that people were also in your shot. This was always a pain for me and drove me nuts. ND filters to the rescue!

Without a Neutral Density filter, you may only be able to open your shutter to ½ a second which leaves a blurry ghostly figure moving through your shot. With the ND filter and a longer shutter speed that person now vanishes from the shot totally! Provided they’re not just standing around. They need to be moving through the image for this to work, but still, it’s pretty cool!

Additional uses for Neutral Density Filters

Let’s say you’re shooting a wedding with a film camera. You start indoors (low light) with a fast film, and then you move outside where it’s too bright for the film you have even after changing the shutter speed and aperture. Instead of wasting the rest of the film you can use a Neutral Density Filter to reduce the brightness of the scene. I know, I know, you probably don’t use film anymore.

When you use a flash your shutter speed will usually max out at 1/250th a second. If the subject is too bright (and you can’t reduce the flash output) you’ll have to stop down the aperture to f/8 or higher. This limits your ability to get a shallow depth of field. Using a neutral density filter can give you that creative exposure you need when using a flash.

You may also want to use a ND filter if your camera is fully automatic since it can provide you with some additional versatility that you didn’t have before. Get a Neutral Density Filter now so you too can control light and improve on your photography.

Graduated Neutral Density Filters (or ‘Grads’ for short)

Graduated ND filters are the same idea, but instead they are a mix of ND on one end and clear on the other with a gradual transition between the two.

Usually the luminance level of a mid-day sky is about two stops brighter than the foreground beneath it. If you were to properly expose for the foreground your sky would be overexposed by 2 stops. If you expose for the sky, your foreground would be 2 stops underexposed. Because of this your exposure is out of balance.
If you take a ND4 (ND 0.6) Graduated filter  and align the ND with the sky, the foreground will then be covered by the clear half leaving it unaffected. Now your exposure is balanced over the entire scene.

Here you can see how a Graduated Neutral Density Filter can balance your exposure:

No Graduated filter

No Filter

Graduated Neutral Density Filter

Graduated Neutral Density Filter

The transition area, or edge, is available in different variations (soft, hard, attenuator). The most common is a soft edge and provides a smooth transition from the ND side and the clear side. Hard edge grads have a sharp transition from ND to clear and the attenuator edge changes gradually over most of the filter so the transition is less noticeable. Here’s where you can find Graduated Neutral Density Filters.

Mounting Neutral Density Filters

You can get ND Filters that screw on to the front of lenses or slide into a mount attached to your camera. And if you’re in a pinch you can just hold it in front of the lens too. One advantage of using a mount is the ability you have to align the edge (or transition) of a ND Grad filter. This allows you to choose where you would like the horizon in your shot, especially if you have a hard edge.

TIP: If you get the type of filters you screw on buy for your largest diameter lens and buy step up rings. These cheap rings allow you to attach the filter to smaller diameter lenses. This option is much cheaper than buying multiple sets of filters. Neutral Density Filters are great when it comes to controlling light. Get a Neutral Density Filter now so you too can control light and improve on your photography.

Categories: Photography

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  1. julie says:

    I’m new at using SLRs, so, Ive been trying to understand how the ND works..
    thanks! very informative!!

  2. Michael says:

    I second Julie’s comment. A very helpful explanation of ND filters. Thank you.

  3. Nandith from India says:

    This article is of great help! Thanks a ton Austadpro.

  4. Alan says:

    Thankyou for making this so easy to understand.

  5. Alan says:

    Thankyou very much for showing how easily these filters can be applied to everyday situations.

  6. Benno says:

    Currently, I’m planning to buy two different ND filters, the normal one and the graduated one.
    As for the normal one, I’m still deciding which to buy, 1.8 or 3.0. My goal is to make nice movements of clouds and also milky and smooth water movements. In those cases, 3.0 is needed? or is 1.8 sufficient?

    Step-up ring should be used to avoid having filters for lenses with different sizes. I agree with that. As far I understand, graduated ND filter can be moved in circles like a CPL. How can you do that if having step-up ring?

    The last question, there are several kind of colors for the dark part of a graduated ND filter. Which one is worth buying?

    • Austadpro says:

      Hey Benno, The 1.8 should be more than enough. It’s a reduction of 6 stops. Don’t forget you can also close your f/stop too. In the photo above of the waterfall I’m using a 1.2 ND Filter. I believe I combined a 0.3 and a 0.9 to get the 1.2.

      The step-up ring doesn’t affect the rotation of the filter, it’s just connects it to the front of the lens. The rotation is part of the filter itself and the transition is centered, so you just line up your shot with the horizon.

      I’m not sure what you mean by ‘dark parts of a graduated ND filter’, but I would look for one with no color shift.

      Hope this has been useful.

  7. Benno says:

    Any GND has a clear and dark part, and there are several kind of colors for the part part. From what I see, it seems most GNDs have color instead grey color. Which one should I consider?

    I forgot to ask you this: Would Cokin kit system be better compared to circle filter? That way I don’t need to buy circle filter for different filter size.

    I found several Cokin 0.6 GNDs, however I couldn’t find square ND filter (not GND) at least 1.8. Most are ND2, ND4 and ND8.
    The way I can think of is two ND8 filters. When using them together, it would be ND64? Add up number or multiply in this way?

    Or how about using Cokin system for GND and circle filter for ND?


    • Austadpro says:

      Use the grey GND filter unless you have a reason to use red. Grey want give you any color change. Either square or round filters work. It really depends on what you plan to do with it. Square filter systems let you adjust the ‘horizon line’ of a GND without moving the composition of the lens (especially if you have a hard transition line verses a gradient transition from grey to clear). For the average photographer, moving the camera lens is sufficient. Square systems provide added flexibility, but are also bulkier. For me, I’m willing to trade the that additional flexibility so I can carry the filters easily in my bag while traveling or on shoots. I like to travel light since I do mostly landscapes. If I was doing studio work, they the square system would be better.

      If you need a ND64, then you can use 2 ND8 filters combined. Reference the chart I have in this blog post for more detail.

      Square filters also work with all your lenses. So you don’t need the step up rings. Technically the gap between the filter and the lens can cause a lens flare, but it’s likely minor, and you should be blocking that light anyway with your hand or a flag. So it really isn’t an issue.

      Resin is just a type of plastic. Yes, glass is better than plastic, but plastic is also lighter. The difference in quality isn’t huge. If you are doing high-end or specialty photography, then that may matter, but again, for the average photographer, you wouldn’t see a difference.

  8. Benno says:

    First I thought about filter ring but then thought I better buy a filter I can use on lens with different sizes,
    and thought about the Cokin ND Graduated Filter Kit, such as,
    “Cokin ND Graduated Filter Kit P Series, with Filter Holder & Graduated ND Filters #121L, 121M, 121S)”

    This is plastic. Is a glass better? If so, why?

    Also, I saw two different kind of Cokin Filter kits, P series and A series. I couldn’t figure what the difference is.
    I presume those filters are square. If so, is a rectangle one better?

    I wonder if there is a gap between adapter ring and filter holder that could cause flare or other distortion?

    By the way, what is a resin filter?

    With the dark part, I mean the dark part of a GND filter besides the clear part. What filter color should I consider when it comes to dark part? There is grey and reddish color.

    Thank you.

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