And How to Get Most Out of It
ND filter is a must-have accessory for serious landscape photographer. I personally love them very much. In this post, you are going to learn how to choose the best ND filter and how to get most out of it.
Table of Content
What is ND Filter?
First of all, let’s talk about what a ND filter is. ND stands for Natural Density. ND filter is a filter that helps reduce the light entering the camera, which also means that it allows you to use a slower shutter speed.
In other words, you can go for long exposure.
Since it can only let the minimal amount of light to hit your camera sensor. The more powerful the ND filter is, the more light can be trimmed down.
So what can ND filters do?
ND filters have the power to lengthen your exposure time. But why do you want to do so?
Using long exposure can give a dramatic effect to your photo. While your shutter is being released and objects are moving in the scene, you will capture the motion of them.
An image speaks a thousand words. I am going to show you four examples of stunning images that were captured by the technique long exposure.
Silky Feel Water Fall
ND Filters vs Small Aperture
If you know the exposure triangle well, you’d know that closing down the aperture or lowering ISO can also lengthen the exposure time.
However, there are limitations for these methods.
Smallest Aperture is Only f/22
In most of the lenses, the smallest aperture is f/22. Some macro lens may have f/32, but it doesn't really make a big difference.
For example, your metering tells you that you need 1/400 at f/8, ISO200 with naked lens, and you now want to capture the wave movement for 1 second.
Without any ND filter, what you can do is to close down the aperture and lower the ISO. In this case, the maximum aperture you can go is f/22, which will give you 1/50 sec exposure time. You may even lower the ISO to 100 and 1/25 sec is what you can get.
So you have reduced 4 full stops by going from f/8 to f/22 and ISO200 to ISO100. But there are still 5.7 stops to go to 1 second. Exposure is calculated by exposure calculator.
In other words, without ND filter, you can't actually reach 1 sec of exposure time!
Tiny Aperture Creates Diffraction Effect That Lowers Image Quality
Another problem of using tiny aperture is that it will lower the sharpness of the image. The following video from Photigy shows you the detail about physics behind diffraction and how it affects your image quality. If you don’t have time to watch the whole video, just simply jump to the last part seeing how ridiculous the image quality at f/32 is.
To conclude, even if you could reach the shutter speed you want, you may still be scared by such a low sharpness.
In order words, ND filter is what you need to have to do long exposure.
Choosing the Best ND Filter
There are two main systems of ND filter in the market: screw-on and slot-in.
- No light can enter from the edge
- Do not require an adapter
- Lower start up cost
- Less bulky and lighter
- Various size is required for different lens
- Vignetting may occur on wide angle lens
- Cannot adjust for graduated ND
- Cannot use on ball head lens like Nikon 14-24mm
- Can use on every lens
- Minimal vignetting
- Easy adjustment for graduated ND
- Require a adaptor
- Higher start up cost
- More bulky and heavier
- Light may enter from edge and affect image quality
Personally I recommend to get a slot-in system because of a few reasons. Firstly, you don’t have to buy a new filter, which is normally quite expensive, as you upgrade the lens they have different screw sizes, hence different filters. Secondly, most wide angle lens are in ball-head shape and ND filter is normally used in wide angle lenses. Thirdly, it is usually cheaper to get a square glass instead of a circular one.
Strength of ND Filter
ND filters come with different strengths, i.e. the power of trimming down light intensity. A stronger ND filter will let you use a longer shutter speed.
There are a few format of ratings, please go to here for detail.
ND Notation 1
ND Notation 2
Comparison of Different Strength
- Almost useless
- Start to have silky feel on water falls
- Ability to remove crowds
- Smoothen the sea or lake
- Capturing cloud movement
- Create fog effect on rocks in seascape
There are lots of ND filter manufacturers in the market. Some of them provide cheap filters but low quality. Some may have reasonable quality but over-priced. Below are some manufacturers I recommend.
For Screw-on System
- Highest Glass quality
- Minimal color cast
- High price
- Decent glass quality
- Minimal color cast
- More affordable
For Slot-in System
- Highest glass quality
- Minimal color cast
- Both 100mm and 150mm slot-in size
- Hight glass quality
- Some color cast
- Both 100mm and 150mm
Special Types of ND Filters
Graduated ND Filter (GND)
Graduated ND filter is a kind of ND filter that half of the filter has no power of light reduction. Half of the filter is in black and half is transparent. It has the ability to just darken half of the sense.
Photographers like to use graduated ND in high dynamic range’s landscape so that they can get all detail in one shot.
However, its limitation is that you can’t use it when there is no horizon line in your photo. Since it is a straight line graduation, you might get a tree which is dark on its upper part but lighter at its lower part.
Most importantly, graduated ND is so much more expensive than normal one. Therefore, you better use the black card technique or HDR to save some money.
Pro Tip: Circular NDs open up a lot of interesting possibilities for things like dragging out exposure times for things like clouds or cars. Grad NDs are an essential tool for any landscape photographer. It lets you block out light from just part of the photo, say the top or side, allowing you to take high quality shots in a single exposure rather than resorting to more complicated editing techniques like HDR.
Photographer at O'TierneyPhotography
Variable ND Filter
I strongly recommend you NOT to use a variable ND filter. Although it seems convenient that you can have various ND strengths in just one filter, you are not only sacrificing the image quality, you are also wasting money on them.
Variable ND filter is normally made of 2 CPL. By changing the angle of 2 CPL, you will get different ND power. You may use it at low ND power, say 1 to 4 stops. In higher power ND, you definitely do not want to go for this type of filter.
The image quality will be so low that you don't wanna look at it because there will be serious vignetting on the image. Some filter may also have uneven darkening power which I have experienced before. Also, even the expensive one (more than USD100) does not have 10 stops power.
Steps to Use ND Filter
Pro Tip: You cannot focus with ND filter installed on the lens, so the focus should taken before you install the filter. Perform auto focus on the area you want, switch your camera to manual focus. Before you shot, you must take the next step: cover the viewfinder, through the viewfinder, light can penetrate and damage the picture.
Blogger/Photographer at Dramatic Photography
Best Practices of Using ND Filters
Get a More Powerful ND Filter
In real life, budget is everything. If you do not have an enough budget to get a few ND filters with different strength, you may just get one with higher strength, say 6 stops or 10 stops.
When using a ND filter for long exposure, most of the time you will find it doesn’t have enough ND power. You can always open up the aperture or increase the ISO to compromise a slow shutter speed. However, you can’t close down the aperture and lower the ISO to make the shutter speed even slower because you are already have the smallest aperture and lowest ISO.
Use All Methods to Stabilize Your Camera
When doing long exposure, vibration is really annoying. Any tiny vibration or camera shake may cause the image blur.
Using a good tripod can minimize the chance of camera shake. Also, using both a shutter-releasing cable and the mirror lockup function together can eliminate all the smallest shake during exposure.
Do find shelter if the location is windy. Strong wind may blow your camera. Make sure you find somewhere to hide from the wind.
You don’t want to find the image blurred and all the effort is wasted after going home.
Pro Top: Always rely on the histogram instead of the camera LCD. If you shoot raw, another good advise is to customise the camera WB driving up the temperature (about 9000K / 10000K). This will remove the “cold cast” of “strong” ND Filter like Big Stopper and will provide a good LCD preview of the final result right in the field
Photography at CarlosResendePhotography
Using ND Calculator or Apps
Unless you are a Math genius (like me :D), you may not be able to calculate the correct exposure time in a short time. Some calculator apps come in handy.
Be Patient and Try Different Settings
Getting the best ND filter doesn't mean that you would also be given the best skill to manipulate it. Therefore, do spend some time to master your filter, hence to master the long exposure.
You have to get familiar with what shutter speed is required to get a certain feeling. For example, you would need around 2 to 5 seconds to get the silky feel for water falls, 10 to 20 second to remove crowds, 1 to 2 minutes to capture cloud movement. These numbers come from my experience. With your experience, you may come up with you own set of numbers.
ND filters may not be easy to apply at first. However, once your get familiar with your filters, you will find that taking stunning photograph is not as hard as you think.
Pro Tip: Watch out for any blue hues or other hues that the photo may suffer from as a result of the filter, and make sure to fix this in post processing.
If you are serious about long exposure landscape photography, I strongly recommend you to check out these two e-books:
Written by the New Zealand photographer Todd. Although using ND filter and long exposure are not the main focus in the book, you can learn lots of landscape photography skill, ranging from basic setting to advance post processing. Most important thing is that you can learn how to compose a great landscape shoot by viewing Todd’s photographs.
If you are serious in learning long exposure photography, this ebook is what you should get. It is easy to read, neat and short, and all the topics that you need to know about long exposure photography with ND filters are included.