Let’s face it, ND (Neutral Density) and ND/PL (Neutral Density Polarizer) filters can be expensive. Should you buy some for your drone?
Short answer. It depends.
Before we talk about ND filters, we should probably first explore exposure in photography.
Aperture, Shutter Speed and ISO affect the amount of light that makes its way to the camera sensor.
The aperture represents the size of hole in the lens through which the light passes.
The shutter speed represents the amount of time that light is allowed to hit the sensor.
The ISO represents the sensor’s sensitivity to the light.
These three settings ultimately control the look and feel of the image.
When taking photographs on a normal sunny day, your camera will probably shoot 24 fps with a shutter speed that is faster than 1/1000th of a second. The fast shutter speed limits the amount of light hitting the sensor to an extremely short burst of light.
While this will typically help get a good exposure for a photograph, with cinematography the composition will probably look unnatural, choppy or jello-like. It will lake that subtle motion blur that is common in cinematic films.
To achieve this cinematic look, we must decrease our shutter speed. The 180 degree rule suggests that the shutter speed around double the frame rate. So if you are shooting at 24fps, then the shutter speed should be around 1/50th.
This will allow light to hit the sensor for a longer time, which will overexpose the image unless we compensate by adjusting the aperture.
That is fine if we are using a dslr, but on some drones like the DJI Mavic Series, the aperture is fixed.
To get the cinematic blur we want, we have to overexpose with makes color grading difficult.
This is where a ND filter comes in. The purpose of an ND filter is to reduce the amount of light passing through the filter.
On a mavic we cannot adjust the aperture, but we can essentially put sunglasses on the lens. The longer the shutter speed or brighter the environment, the darker the sunglasses / ND filters we will use to get the correct exposure.
By using ND filters on the drone for cinematic shots, we will get that nice buttery motion blur.
If, however, we are just taking photos and motion blur is not important to the desired composition, then an ND filter is not really needed.
In summary, ND filters help you achieve a pleasant motion blur for cinematic shots but probably aren’t needed for most photographic shots. So, the decision to buy or not buy, comes down to what you are trying to accomplish.
One final thought about ND filters, is that like when buying filters, low quality filters tend to hurt image quality so it is usually a good idea to get quality filters.
You may also be interested in my article on ND vs ND Polarized filters for drones.
What is your experience with ND filters on your drone? Let me know in the comments below.