ND filters are the best-selling accessories for a drone; any serious user should own a set, but there is often confusion about how to use them and why
In this article, we will see if and why you need ND filters for shooting footage, hyperlapses, and photography with the DJI Mini 5 Pro. I will also suggest which one to use for the different occasions
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What Are ND Filters
The name ND stands for Neutral Density. The purpose is to reduce the amount of light entering the sensor without affecting the hue or the color rendition. In other words, they act like sunglasses for the lens.
But why do we want to reduce the light? The Mini 5 Pro with its 1” sensor and f1.8 aperture collects plenty of light, which is an important feature in most situations
However, when shooting footage or photos in the middle of a sunny day, the amount of light collected will result in an overexposed image, even when selecting the base ISO and the fastest shutter speed, 1/8000”. An ND filter solves this issue by reducing the amount of light entering the sensor
On other occasions, we may want to apply a specific shutter speed, for example, 1/50”. However, the luminosity will often be too strong, resulting in an overexposure. To apply a specific shutter speed in any light conditions, we must use an ND filter of the correct value
For Video
There are three exposure parameters:
- ISO
- Aperture
- Shutter speed
With the Mini 5 Pro, as with most DJI prosumer drones, the aperture is fixed, so we have only two values to consider
For ISO, in most cases we want to keep the minimum value of 100; however, the Mini 5 Pro performs very well with values up to 800 without any noticeable quality degradation, so there is some room for maneuver if needed
The most important value is Shutter speed. According to the famous 180-degree rule, when shooting video, it is suggested to use a Shutter speed of 1/50” with a frame rate of 25 or 24 fps, 1/60” with a frame rate of 30 fps, 1/100” with 50 fps, and so on
This is because these values apply some motion blur to moving elements, mimicking how we would see them in real life
Let’s see an example of moving elements with the correct shutter speed compared with others using a much higher value. As you can see, with a fast shutter speed, the elements in motion look jumpy, too sharp, and unnatural
The correct shutter speed is especially important when the scene contains moving elements at a relatively close distance, or when flying fast close to the ground. Motion blur is not a concern when filming landscape footage with a drone at a high elevation far from moving elements
Professional users tend to use manual exposure to control the shutter speed and apply the correct ND filters for specific light conditions before taking off
However, for video, the Mini 5 Pro offers a Dual Native ISO mode with enhanced dynamic range. This mode is only available with Auto or semi-auto exposure. The Dual Native ISO mode is a good reason to use Auto or Semi Auto exposure, even for experienced users
When using automatic exposure, we can apply a filter that maintains the shutter speed close to the optimal value
The set of filters I use is the Freewell All Day 6 pack with filters ranging from ND 16 to 1000, covering all sorts of situations. When shooting footage, I tend to use the intermediate values, ND 64 or ND 256; we can compensate for the gap between the filters with a small adjustment of the ISO value
For Hyperlapses
For this technique, the correct amount of motion blur is crucial. I would not even consider attempting a time lapse or hyperlapse without ND filters
A common mistake beginners make with hyperlapses is disregarding the importance of the correct shutter speed. In these examples taken without ND filters, the result is a disaster, unwatchable, especially when the scene contains elements in motion, which is, in most cases, the point of a hyperlapse.
If we compare them to others taken at the correct shutter speed, we immediately understand why ND filters are needed
According to the 180 rule mentioned above, we should use a shutter speed of one second with an interval between photos of 2 seconds, 1.5” with an interval of 3” and 2” with an interval of 4”
But with drones, we don’t have the same flexibility as with ground-based cameras. Shutter speeds slower than 1” are not always available in the hyperlapse setting; also, the aircraft is not as stable as a camera on a sturdy tripod, so a very long shutter speed can cause unwanted image blur
For hyperlapses with drones, we must compromise and always select a shutter speed of 1”. As you can see, the results are excellent: the moving elements flow smoothly, and the motion blur is similar to what we would see in real life
The shutter speed value of 1” gathers more light compared to the values used for video, so stronger ND filters are needed. The ND filter with the highest value in the DJI set I use for video is ND 1000; with this value, we can use the correct shutter speed for hyperlapse in most situations, except for the central hours of a sunny day, which are to be avoided anyway, as the shadows are very harsh and the contrast too strong
For Photography
In photography, the main reason to use ND filters is for creative long-exposure shots. It is great fun, and the results are often stunning
One way to do it is by having the drone fly. The shutter speed value suggested is again 1”, so we need the same filter as for hyperlapses. The best results are often obtained when flying close to the ground in a straight line toward a target: the idea is to keep the target in focus while blurring the other elements.
Another possibility is with top-down views while ascending or descending. It is better to avoid lateral moves, as everything will be blurred in this case. I suggest experimenting with this technique, as the results are often surprising
But a drone doesn’t always need to be flying. It can also be placed on a solid flat surface and used as a ground-based camera on a tripod, even in urban situations. The Mini 5 Pro can take photos with very long shutter speed values of up to 8”, a new feature compared to previous models. Let’s have a look at a few examples with shutter speeds ranging between 1” and 3”
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