How Does a Variable ND Filter Work?
- Pros and Cons of Using Variable ND Filters
- Circular Polarizer Do’s and Don’ts
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Photo by Matthew Leland from Pexels
A variable ND filter is an interesting piece of equipment. With one, you can dial in a changeable amount of attenuation instead of being held to one fixed amount of density. While many photographers enjoy using these interesting tools, others may have some questions about them.
Should you use a variable ND filter? How does a variable ND filter work? How do variable ND filters vs fixed ND filters compare? Are there any problems with variable ND filters to be aware of? Can you use variable ND filters for video?
We’ll tackle these questions and give you a few tips about variable ND filters and ND filters in general. Let’s start by looking at a good example of a variable ND filter that I’ve been using recently.
Haida NanoPro MC Variable ND Filter
One thing I like to do with specialty screw-in filters is to buy the largest size I need and adapt it to smaller filter diameter lenses. So, for this screw-in variable ND filter, I picked up the 82mm size Haida NanoPro MC Variable ND Filter. You can see it mounted on my personal camera above.
The small handle makes it easy to adjust the variable attenuation and helps you avoid accidentally smudging the glass. Like all Haida filters, it’s multi-coated for reflection control and made from high quality optical glass and lightweight metal. It’s a lot of fun to use.
How Does a Variable ND Filter Work?
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It seems like some form of wizardry to be able to twist a filter and have it slowly darken. What’s happening is called cross polarization. You may have played around before with your filters, mounting two polarizers together and seeing the view go from dark to complete black.
When two polarizing glass planes are both placed within a light ray, the polarization of both pieces can essentially block out most of the light from exiting that optical path.
This is how a variable ND filter works its magic. It is two polarizers mounted together which you twist around on an axis to see the gradual change of light attenuation. Words don’t convey the effect adequately, you’ll have to see it in action.
Learn More:
Should You Use a Variable ND Filter?
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Sure! There are multiple uses that come to mind and not all of them include that awesome motion blur effect, though that is one good reason. So let’s start there. Using a variable ND filter to create the long shutter speeds needed gives you options on just how long an exposure time you get. It also allows for more creative use of aperture along with the long shutter speed.
While motion blur of water and clouds was my first thought when I got into ND filters, another very useful trick concerns aperture. Sometimes, a scene is so bright, I find it difficult to be able to use my portrait lens wide open enough for the selective focus effect. Using a variable ND filter, I can easily balance my creative wants with the exposure needs of the scene.
Variable ND Filters VS Fixed ND Filters
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The whole reason for having a variable ND filter is to enable you to have options of how much density to add without physically changing filters. If that isn’t important enough, a fixed ND will work just fine.
I like to take my filter holder system with a lot of different filters with me when I’m on a nature photo trek. I take just my variable ND filter when I am planning on being more mobile such as an environmental portrait session or doing street photography. They are both valuable choices for my personal needs and style.
Problems With Variable ND Filters
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There isn’t too much to worry about with using variable ND filters in most photographic situations. The main things that might be problematic at times are due to pure physics.
Since a variable ND filter is really two polarizers, you might not get the polarization effect desired for a scene since your variable ND filter is already polarizing the light.
The other problem is that while the filter changes the effect gradually as you twist it, when you get close to the maximum attenuation, it happens very fast. So while it’s slow and gradual about 90% of the time, the density closest to maximum happens with very little extra movement, just something to keep in mind.
Can You Use Variable ND Filters for Video?
Absolutely! In order to achieve a frame rate that appears natural while still using your f-stop for focus depth control, a variable ND filter becomes a must-have tool for videography. Especially when filming in bright light like outdoors in broad sunlight.
Check the video above by Jaren Polin to see what I mean.
It’s a Tool and a Toy
Photo by Lisa Fotios from Pexels
My variable ND filters get quite a workout. I use them in videography all the time and they are my go-to filters for shooting more mobile genres and styles of photography.
Plus, I have to admit, sometimes I just go outside with my gear and play around. I love photography, it has made me happy. Not only do I get to make a living from it, I get to enjoy it as a creative pastime and hobby. As an added bonus, I get to share my fun with you!
