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A neutral-density filter or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colours, of light equally, giving no changes in hue of colour rendition. It can be a colourless (clear) or grey filter. A standard neutral-density filter will reduce the amount of light entering the lens, with colour reproduction not being affected.
A polarizing filter removes polarized light from the image, thus reducing reflections and glare, increase contrast and enhance colours. Polarizer is probably the most useful filter you will ever find, as it helps you capture pictures with attractive colour composition.
Benefits- ND Filter
This filters and polarizers also acts as a protective screen for your drone's camera lens. ND filters are used for managing difficult light condition. It can block excessive light giving us control over exposure time, aperture, sensor sensitivity, etc.
ND filters are also used to fix Jello effect, a choppy footage that looks more like a cheap cam than quality videography.
With ND filters reducing the amount of light that comes in contact with the sensor, you will be able to film at slower shutter speeds (like 1/50th of a second, 1/60th of a second, 1/120th of a second,) and a lower aperture. This will also create motion blur, thus helping you achieve a smoother cinematic video.
Benefits- Polarizer Filter
Polariser reduce reflection from subjects or objects, enhance colours, etc. giving us control over exposure, colour saturation, etc. Using a polarizer is very necessary to darken skies, manage reflections. Polarizers will remove glare from non-metallic surfaces, such as windows and water.
When to use: ND Filter
LONG EXPOSURE: Long-exposure shots are relatively easy to take at night with a drone. But in a normal sunny day, if you want to capture long exposures you need to set the shutter speed slow. Which means the shutter will be open for a longer time, doing so will allow more amount of light to reach the sensor and overexposed your image. In order to get exposure times ranging from several seconds to minutes, you need to cut out of a lot of light. this is why you will need ND filter.
MOTION BLUR: Next is when you want to create Motion blur. Long exposure is a kind of motion blur too. The problem here is when you slow your shutter speed to blur elements in your image, there's a chance that too much light will enter and overexposed your image, same as in the case of taking long exposure. So you need a ND filters. Motion blur can sometimes make your photo look natural.MOTION BLUR IN FILMAKING: Motion blur takes its part in videography too. The idea of motion blur was brought to help blend frames and imitate the blurring that occurred normally, due to objects moving quickly.
In cinema, the standard frame rate is 24 fps. And the ratio of frame rate to the shutter speed should be 1:2 for a smooth cinematic video. This means, if you want to shoot a video at 24fps, then shutter speed should be 1/50th of a second. Similarly for 60fps, Shutter Speed should be 1/120th of a second. And if you want to shoot a slow motion video at 120fps Shutter Speed should be best at 1/240th of a second. This relation between fps and shutter speed is known as the standard 180-degree rule in the film industry. This is similar to how human eye experience motion in real life.
Most drone cameras came with high speed shutters up to 1/8000th of a second, so we're able to nearly eliminate motion blur, each frame is like a perfect still moment in time. This is exactly what stop motion videos are. But if the motion is smooth, each frame is a perfect moment in time. The video will look more pleasing and natural when you watch. You should also keep an eye on your ISO to limit noise.
BALANCE EXPOSURE: Another case would be to balance exposure. When you want to capture an image, but the contrast in exposure is very high such as bright skies and somewhat dark landscapes like capturing sunsets, sunrises and scenery with mountain ranges.
Some drones has fixed aperture, (like DJI Mavic air, DJI spark has fixed aperture f/2.8 and f/2.6). For this types of drones in a sunny day, the footage will be bright and flat, because of the fixed aperture f/2.8, which means your aperture is wide open, so more light can enter. Even if you want to follow the above cinematic rule, you should not. As lowering the shutter speed, like 1/100th of a second, would lead more light to enter, resulting to an overexposed image. So a ND filter will help you in these problems.
Whenever you feel like you need to cut down some exposure, you can use ND filters.
When to use: Polarizer
You can use a polarizer whenever you want to reduce glare from objects, punch up colours and increase contrast. When you want to capture image/videos with attractive colour composition, polarizers are very necessary.
An example would be, let's say you want to take a photo/video of the beach and blue water, or you want to capture an aerial view of a park where there are trees and stuff. On a sunny day, you'll notice that the image doesn't convey what you're seeing; the water doesn't look as clear and it has a shiny surface, the scenery of the park looks flat. By using a Polarizer (PL), you will be able to remove the unwanted glare and bring back the colour of the water. By using a PL, you will be able to bring back the colour saturation of the trees and the sky.
Types of ND Filters
There are also certain types of Colour Filters which are used for colour correcting and to change the mood of pictures such as cooling tones and warming tones.
Graduated Neutral Density Filter (GND): The GND filter is an ND filter that allows transitions from light to dark. The main purpose of the GND filter is to balance exposure in an image that contains a bright sky and relatively darker foreground. Landscape photographers are big consumers of GND filters and they perform especially well when capturing sunset images.
ND filters are classed by their optical density or equivalent f-stop reduction (number of stops).
The exposure time given in the above table is not accurate as there is difference in quality of the glass of different filter manufacturer. You can grab the idea that with higher f-stops you can get a longer exposure time.
Most manufactures use one of these described ND numbers or optical density to describe their filters. The ND2 has an optical density 0.3, so it is also called as ND0.3. It provides 1-stop of light reduction and say, when your camera's original exposure is limited to 1 sec, the ND2 filter can extend the exposure time to 2 seconds.
A ND4 filter results in a 2 f-stop reduction. This means you will need to quadruple the exposure time if you stay at the same aperture setting for a correct exposed image. And so on, you can read the table above. A ND8 filter will result in a 3 f-stop reduction, thereby leading to an 8 times longer exposure. And so on.
Which filter should you use
As choosing a filter totally depends on weather conditions, I cannot tell you exactly which ND filter to use. The more higher ND number you use, the more light it can reduce, and gives more exposure time capability.
ND4/PL or G-ND4 can be used for shooting golden hours. ND4, ND8, ND16 are most frequently used ND filters. A 5-stop ND filter (ND32/PL) should be perfect for slowing your shutter speed enough to slow smooth motion in mountain streams and waterfalls.
ND64 filter is for use in extremely bright conditions and provides 6 stops of light reduction, you can use this for shooting in desert with bright sand.
Higher rated ND are used very specific to what we want to capture. The ND1000 which provides 10-stops of light reduction. Darker ND filters are popular for extremely slow shutter speed shooting and extremely wide aperture shooting under bright sunlight.
Again it always depends on the weather condition, there are many different apps that can give you information about weather condition specific to your area. Use some, try different filters and see what would suit best in your condition, before you put the bird up.
Available filters from CLELO
CLELO has filters for drones: DJI– Spark, Mavic pro & platinum, Mavic 2 Pro & Zoom, Mavic Air, Phantom 2 Vision+, Phantom 3 Pro & Advanced, Phantom 4, Phantom 4 Pro & Advanced, Inspire 1, INSPIRE2.
Other than drones, we supplies filters for Action Cameras like DJI- OSMO, HD Cameras like Panasonic Lumix 15mm f/1.7, Olympus M.ED 12mm f/2.0, Olympus M.Zuiko 17mm f/1.8, Olympus M.Zuiko 25mm f/1.8, and much more. For further details, please feel free to contact us.