In this article, I will discuss on an important topic in photography. Although this can be treated as an intermediate to advanced technique, but I will try to keep it as simple as possible making it seem like a piece of cake to all my readers.
ND stands for "Neutral Density".
ND Filters are useful in certain area of photography where you are looking for a specific type of effect under adverse lighting conditions.
Ok, ok. Let me break that down for you.
What do you do when you go out on a sunny day and you know you are going to spend a lot of time outdoors? You get a cap and a sunglass. That's right. You want to counteract the effect of direct sunlight so that you are not "blinded".
Camera works in a similar way. But not EXACTLY the same way as we are not "blinded" by continuously looking at a moderately lighted scene. Let me explain more on camera terms with an example.
Say you are taking a photo of a waterfall and you want to have that "creamy" and "silky" effect of the flowing water.
Here's an example photo: (For full-size photo, see note at the end of this article)
The key to this type of photo is to set a slower shutter speed to get that "motion blur" in flowing water thus giving the dreamy silky effect.
Here's another example: (For full-size photo, see note at the end of this article)
The enemy of a slow shutter speed is the ambient light. Just try this experiment: Put the camera on a tripod in P mode. Making sure the flash is off, point your camera towards any object and press the shutter "half-way" and record the shutter speed setting and aperture setting which is automatically selected by the camera. Now change the mode to M and select the same shutter and aperture. Take the photo with this setting, it should not come out that bad. Now the fun part, slowly reduce the shutter-speed one by tenth of a second at a time and see how the photo looks. You will notice the photo is becoming brighter and brighter and at a point everything is so bright that nothing can be figured out clearly. Pros refer to this condition as "blown-out" photo.
The above is an example of "increasing the exposure" by reducing shutter speed.
But say, you NEED slow shutter speed to get that motion blur. Of course, you can reduce aperture. But how much? F16, F22, F39? There will be a situation in broad daylight when you have the aperture set to the camera supported minimum, and still you are not able to lower the shutter speed enough to get that motion-blur without "blowing-out" the photo. Yeah, yeah, now we are talking photography.
One more example: (For full-size photo, see note at the end of this article)
You wish somehow if you can reduce the amount of light reaching the camera sensor, so that the photo does not blow-out and yet you can comfortably reduce the shutter speed to achieve the motion-blur AND at a decent aperture setting.
Ladies and gentlemen, welcome ND Filter.
This acts like the sunglass on your eyes, limiting the amount of light that reaches the camera sensor, "eating" up light so that you can take photos in broad daylight and still set the shutter speed as slow as ~1sec (can you believe it? the flowing water will be as creamy as ever) at a reasonable aperture of ~F22.
Standard settings I use for silky/creamy water flow effect putting the ND filter on:
- Mode: Shutter Priority (Tv)
- Shutter Speed: start with 1/10 secs and reduce it gradually till you get the desired amount of blurriness effect
- Aperture: F13-22
- ISO: 100 or lower
- White Balance: AWB or Cloudy
- Metering Mode: Evaluative (if I have bright area in the scene, I do a partial metering)
Consider another situation, where you want to focus only on the subject keeping the background out of focus, so you widen the aperture to the smallest value your camera/lens supports (say F2.8) and guess what, the photo becomes "blown-out". You try to increase the shutter speed, but alas, even the maximum supported shutter speed is producing a "blown-out" photo. You guess it right, ND filter is again our rescue crew. Put on a ND filter and you can keep the minimum F-stop with a reasonable shutter speed and still get the subject in focus with rest of the scene out of focus (I am deliberately avoiding the concept of Depth-of-Field to keep this article simpler, more to come in future articles).
Of course, you can try lowering the ISO to 50 or lower, but the effect of reduction of light, by lowering ISO sensitivity is very negligible compared to ND filters. What I mean is lowering ISO is no match against the ND filters in reducing the impact of "amount of light" on brightness of the photo.
Types of ND filter
There are different types of ND filters available and are classified based on the amount of light it blocks (or the darker/denser the glass is).
The greater the optical density, the more light it will absorb. So a ND filter is sometimes classified in terms of density
0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0 and so on.
The light blocking capacity of the ND filters are also measured by the reduction of f-stops. The more f-stops a ND filter will reduce, the less light it will allow to pass. Thus a 2-stop ND filter will block double amount of light than a 1-stop ND filter.
So this is one way of specifying the "darkness" of the filter. There's another.
Different manufacturers use different conventions. ND4 filter means a 2 stop ND filter. Confusing? Heh? A little bit of math here...
ND2 means 1 stop ND filter (2=2 to the power 1) allowing 50% light to pass (transmittance)
ND4 means 2 stop ND filter (4=2 to the power 2) allowing 25% light to pass
ND8 means 3 stop ND filter (8=2 to the power 3) allowing 12.5% light to pass
and so on..
And here's the chart that links the density and stops
0.3 ND filter = ND2
0.6 ND filter = ND4
0.9 ND filter = ND8
and so on...
If you are a little bit lost, do not worry, all you need to understand is that "darker" ND filter will block "more" light. ND8 is darker, ND2 is less dark. 0.9 ND Filter is darker and 0.3 ND filter is less dark, 3 stop ND filter is darker and 1 stop ND filter is less dark and so on and so forth. That should work for now.
Which one to use and when?
The ND Filters you will need will depend on how much light you want it to absorb so that you can achieve the desired shutter speed or the desired aperture size at the ambient lighting conditions (remember the first statement in this article?). Hence this depends on how much ambient light you are working in. So overall this is more or less experimental. The thumb rule is - If you want a lot of motion blur or absolute silky-ness, use the darkest ND filter (ND8) so that you can really slow down the shutter. If it's dark (overcast, dawn or dusk) you may not need the darkest ND filter because already there is less light. So you may try a medium dark one (ND4) to achieve the same effect. For sports, to bring that motion blur, you may need just a slight dark one (ND2) if don't wan't "too" much blurs.
Do I really need ND filters?
You will most likely need ND filters (of various strengths) if you shoot landscape a lot (like me, which you can see in my photoblog, 75% of my best collections are landscapes). Or you shoot sports a lot in bright daylight. But as I said, you will KNOW you need a ND filter when you have reached your camera/lens limit of blocking amount of light and do not have any further option.
A waterfall example: (For full-size photo, see note at the end of this article)
BONUS TIP: You can always "stack" up one filter on the other to increase the "darkness" even more. But beware of vignetting at wide angle shots (18-20mm) with stacked up filters along with other "combination" effects.
How many do I need to buy?
Well... in my opinion get hold of a 0.9 ND Filter FIRST and then if you need go for a 0.6 ND Filter. Then you can stack them up to get even darker ND filter. I have rarely used my 0.3 ND Filter till now.
When NOT to use the ND filter
A word (or sentence) of CAUTION: Most ND Filters are effective only on the visible spectrum of light and does not proportionally reduce ultra-violet or infra-red radiation. This can be specially dangerous if you are using ND filters to view sources like sun or white/red hot metal or glass which emit intense non-visible radiation which are not blocked by the ND Filters and can seriously damage your eyes as the source does look dim when viewed through the filter. Do NOT look directly at sun through the viewfinder even with a ND filter. You eyes are precious, specially if you enjoy photography. Lol.
Another situation to avoid using ND-filter is when the scene has a mixture of areas with higher and lower brightness (i.e. not uniformly lit). For e.g. during a sunset the horizon is bright but the ground is dark. Using a ND-filter will make the darker spots more dark thus losing the appropriate detail (this is opposite to "blown-out" and is called "burn-out").
What are the available varieties? Which one to choose?
There are different flavors of ND Filters that are available in the market. To start with I would always suggest to go for a "Multi-coated" ones as they are better quality than a normal glass and worth the price. The normal glass ones are cheaper and has a lot of side effects (color-casts) associated with it. Of course there are "Pro" ones that cost a lot, but then they are durable, scratch resistant and best quality.
Options include different brands like Hoya, Single Ray, B+W, Tiffen and Lee filters. These are GREAT filters with no color casts but the cost varies with make and model. I own Hoya filter sets and I am quite happy with the quality of the light reduction and at a reasonable price. Single Ray filters are relatively very costly but with high optical precisions. In my opinion, for experimental learners, I would recommend getting a hands on Hoya filters.
Why are these sunglasses for camera called "Neutral"?
Good question. Because these sunglasses (should) "eat up" light of all wavelengths equally. This means during absorbing, no color is given preference over the other. Thus the term "neutral". But not all ND filters in market are made perfect. Specially the cheap ones that create color casts in recorded photos as they cannot reduce intensity of all wavelengths equally. So I would recommended getting standard, branded and quality ND filter (the multi-coated ones). Research on the internet, read reviews and forums to find out the best ND Filter that will suit your needs and your pocket. If you would like to read my suggestions, you can visit:
That's all for an introductory article on ND filter. Get one and enjoy your photography spree.
Talk to you soon,
P.S>> All the images used as samples in this article can be viewed full-size at this link: http://www.pleasurephotography.com/nd-filter-guide
Visit the Author's website: http://www.pleasurephotography.com