What is a Variable ND Filter?
Variable Neutral Density (ND) filters are like sunglasses for your camera. Sounds cool right? But why on earth would you need sunglasses for your camera?! The answer is simple, and is directly related to videography - which we’re all doing these days, right? So, what is a variable ND filter, and why should every videographer (and aspiring videographer) purchase one? Let’s start with a bit of knowledge on how you should be setting your camera up for videos if you’re looking for a true cinematic look.
To shoot cinematic videos on your mirrorless camera, most videographers recommend shooting at 24 frames per second (fps) or 30/fps. There are some exceptions (120/fps is ideal for slow motion), however, for the most part, you’ll want to stay at these frame rates.
Next, you’ll want to ensure your aperture is wide open (maybe around f/2.8 - f/4.0). This will create a solid depth of field between your subject and the background, creating a nice bokeh, and furthering the cinematic look of your shot.
Are you still with me so far? Ok good, because this is where it gets a little tricky. Next you need to set your shutter speed - but it can’t just be any shutter speed. The rule of thumb for videography is to keep you shutter speed roughly double your frame rate. So, if you’re shooting at 24/fps, you’ll want a shutter speed around 1/50. If you’re shooting at 30/fps, you’ll want a shutter speed around 1/60. This is known as the 180 degree rule.
Now setting your shutting speed to double your frame rate is in theory very easy, but the difficulties come when you’re out in the field - especially when you’re shooting videos on a sunny day. This becomes very apparent if you’re also using a wide open aperture too. Why? Because a slow shutter speed combined with a wide open aperture means your camera is letting in a lot of light, which, in bright sunny conditions, overexposes your videos. So, how do you maintain the correct frame rate, shutter speed and aperture to ensure you’re getting cinematic shots without overexposing your videos? Use a variable ND filter.
ND Filters solve the problem of over exposed videos. They are essentially a dark piece of glass that covers your lense (like sunglasses), making your camera a set number of stops darker (depending on the strength of the filter). So, if you’re camera is set up properly for filming, but it’s over exposed by about three stops, you’ll need an ND filter that can darken the front of the lense by three stops. All of a sudden, you’ve maintained all of those awesome camera settings noted above to keep you shooting cinematic videos, without having a bunch of over exposed footage.
Variable ND filters, as opposed to regular ND filters, make this a lot easier when you’re out shooting. Regular ND filters have a set number of stops (for example, an ND8 filters is three stops). This means, if you go the regular ND filter route, you’d need a bunch of different ND filters with different stops to ensure you’re always ready no matter the lighting conditions. A variable ND filter, on the other hand, allows you to change the number of stops you want to darken your lense by simply twisting the ring of the filter. This means you will have access to a bunch of different ND stops all in one filter.
This is possible because variable ND filters are comprised of two pieces of glass that create different levels of neutral density when they’re twisted. Common variable ND filter stop ranges include 2-5 stop filters, and 6-9 stop filters. I recommend a 2-5 stop filter, as I’ve found that I use that variable ND filter the most on a day-to-day basis.
ND filters and variable ND filters can also be pricey, which is again why I think variable ND filters are the way to go as they are more efficient. Sure, buying one is an investment up front, but you’ll have a number of stops covered with one filter, eliminating the need for a bunch of individual regular ND filters in your bag.
Variable ND filters are a small but powerful accessory for your mirrorless camera if you’re shooting video. They’ll ensure you can stay at the appropriate frame rate, shutter speed and aperture to achieve an awesome cinematic effect, while also keeping your camera bag nice and light. Are you using variable ND filters yet?
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