August 15, 2016

Filming With Your Drone: Why use an ND Filter?

A common question we get from our customers is, “Why do I need a neutral density filter for my drone?”

Aside from DJI’s Zenmuse X5 platform, the aperture on most drones are fixed, including GoPro’s Karma and DJI’s Phantom 4, Phantom 3, and Inspire 1/X3 cameras. To capture a balanced exposure, the camera uses a combination of ISO, shutter speed, and aperture. With a fixed aperture, the only variables left for achieving the correct exposure are ISO and shutter speed. When filming in bright conditions the camera has no other option than to increase shutter speed to properly expose a scene, which results in shaky footage, or jello effect. Adding a neutral density filter will reduce the amount of light that reaches your camera’s sensor, allowing you to manipulate the shutter speed by using different strengths, or stops, of neutral density filters.

Why do I want a lower shutter speed while filming?

Reducing shutter speed is a common cinematography technique, and can be explained by the 180 degree shutter rule. While the this rule is antiquated and explains the relationship of frame rate relative to shutter angle on old film cameras with rotary shutters, we can apply the concept to the digital format, as a simple way to describe the appearance of motion blur in video. By reducing shutter speed relative to your frame rate, you can control the appearance of motion blur. Traditionally, the most common setting in cinema has been a shutter angle around 180 degrees. For digital applications, this translates to a shutter speed at double your frame rate.

For example, on a bright sunny day the camera will be natively firing near 1/1600th, at 24 fps. Without the ability to control aperture, the only way to get your camera to 1/50th (nearest 1/48th) is to use a 5-stop ND filter (ND32). With the ND32 filter you are reducing 5-stops of light from hitting the camera sensor, therefore forcing the camera to drop shutter speed to 1/50th. At 1/50th, you are at the closest shutter speed possible to 1/48thth of a second. By applying the concept of the 180 degree shutter rule, you are creating the smoothest composition possible with your drone.

How do I know which filter to use while filming with my drone?

The first step in choosing which filter to select is to determine what your frame rate is. This number is sometimes referred to as frames per second, or fps. Because the most common frame rate in cinema is 24, often times drone cinematographers will be shooting at 24fps to match the frame rate of the other large production cameras on set. The second step is to determine what the target shutter speed is for your selected frame rate. Your shutter speed should always be as close to double the frame rate as possible, as described by the 180 degree shutter rule. So, if you are shooting 24fps, your shutter speed should be 1/50th. If you are shooting 60fps, your shutter speed should be 1/120th, and so on. The third step is to determine how many stops away you are from your target shutter speed. On your monitor you can see what the camera is natively shooting at, but you will need to be comfortable with how the f-stops are calculated to determine how many stops of light you need to reduce. Once you figure out how many stops of light you need to reduce, choose the appropriate ND filter. Here is our filter reference chart:

Phantom 4 Filter Guide

I have no idea what F-Stops are, so how can I tell which filter to use?

Luckily the team at PolarPro does and has developed a filter calculator app, so you don’t have to do the math. You can download the calculator here: (App coming soon)
It is as easy as entering the numbers you see on your monitor and clicking calculate. The app will then tell you which PolarPro filter is best to use for the current lighting condition.

Why are there so many levels of ND filters for drones?

There are many different types of neutral density filters for the DJI Phantom and X3 platforms, GoPro Karma, and other popular drones because there are many different types of lighting conditions. We don’t make any filters that are for novelty; we make filters that we personally want to use ourselves. We have our stronger ND filters for extremely bright days (ND32, ND64), and we have our lighter ND’s for filming in overcast conditions, or at dusk and dawn (ND4, ND8). In addition to traditional neutral density filters, PolarPro has developed neutral density and polarizing combination filters specific to the needs of aerial cinematographers.

Neutral Density/Polarizer Combination Filters:

For the GoPro Karma and DJI Phantom and Inspire/X3 platforms, PolarPro also offers hybrid neutral density and polarizing filters, which will help to reduce glare and increase color saturation while maintaining proper shutter speed. These hybrid filters will provide a clearer image than the alternative of stacking a ND and polarizing filter, and are light enough that they do not inhibit the performance of the gimbal, requiring no counter balance. While the neutral density filters allow greater control over the camera’s shutter speed, the polarizing aspect of these hybrid filters reduces harsh glare from direct reflections when flying over water, snow, desert, or other reflective landscapes, while sharpening contrast and improving color saturation.

PolarPro Neutral Density Phantom 4 Filter
Photo Credit: Vadim Sherbakov, PolarPro Team Ambassador

Graduated Neutral Density Filters:

PolarPro offers a set of graduated filters, which includes a ND8 graduated filter, a blue graduated filter and orange graduated filter. The ND8 graduated filter is perfect for difficult lighting conditions, such as during the golden hours, allowing you to properly expose the sky without underexposing the ground. The blue graduated filter will add a cooler temperature to the sky without changing the temperature of the ground, while the orange graduated filter will add a warmer temperature to the sky, without changing the temperature of the ground. These filters are perfect for capturing epic sunrises and sunsets, or for adding creative flare to your project.

PolarPro Phantom 4 Neutral Density Filter
Photo Credit: Jimmy Wilkinson, PolarPro Team Ambassador

Why do I need lightweight filters for my drone?

Most drones are outfitted with gimbals that require near perfect balance to operate smoothly. Because the gimbals are calibrated for balance during production without a filter installed on the camera, adding a heavy filter to the camera will put excess strain on the gimbal. By using PolarPro’s lightweight drone filters you allow the gimbal to operate smoothly just like it was intended to do. All of PolarPro’s filters are guaranteed to be light enough for the gimbal they are designed for.

Why choose PolarPro filters?

We stand behind our products with a lifetime guarantee. Furthermore, we have dedicated design and production teams that actually fly and film. With priceless first hand experience and insight to aerial photography and videography, you can trust us to help you capture perfection. If you ever have any questions about our products, we are here to help.

GoPro Karma Filters

What if I can’t get the shutter speed at exactly double the frame rate?

If the shutter speed is not at exactly double the frame rate, then you are in between f-stops. You can either leave the camera in auto mode and not have to worry about color correcting later, or you can really impress your clients or audience, and take manual control of the camera. In manual mode, when you adjust the shutter speed you are also moving the exposure, so your composition will probably be slightly overexposed or underexposed. At this point you can leave it as is, and do some editing later, or you can change the EV compensation to bring you back to a balanced exposure.

What ISO should I use?

Generally, you want ISO to be 100 or as close to that as you can get. The lower the ISO, the less grainy the footage will be. Generally, during the day it is ok to have ISO in the 100 to 400 range, allowing you to dial in the shutter speed.

If you have any additional questions about camera settings or about using our filters, please feel free to give us a call or shoot us an email, we are more than happy to help.

Shop PolarPros range of DJI Phantom 4 Filters Here

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