Source ： http://www.wetalkuav.com/neutral-density-an-awesome-addition/
Three or four years ago, the drone was mostly thought of as a model plane. Now, it’s considered a full-fledged flying camera. Drones have been a huge boon to the film industry, allowing for incredible shots at vastly reduced costs. Many professional photographers have jumped onto the drone scene, drawn by the prospect of shooting images from what some call “God’s Perspective.” A Professional Photographic Tool Recently, Dronestagr.am announced the winners of the 3rd International Drone Photography Contest. This year, 5999 photos were submitted from all around the world. Below are some of these remarkable photos: 
Manufacturers are clearly aware of the demand from the photo and video worlds – and have been pushing hard to up their game. Here, we explore Neutral-Density (ND) filters and their use in aerial photography/videography. Mechanism In simplest terms, ND filters are used to reduce the amount of light that passes through the lens and reaches the sensor. Many users might well wonder: Why bother? 
As we know, exposure can be adjusted by setting the aperture, shutter, and ISO. For example, photographers can adjust these parameters to add motion blur to a subject (think moving water, clouds, people in motion, etc.), change the depth-of-field, and more. But still – especially on days with bright sunlight – there are limits to what a photographer can do. Enter the ND filter. Let’s say it’s a bright day at the beach. Your aperture is set at F11, your ISO at 100. But it’s so bright your shutter speed must be at 1/500 or 1/1000 for a correct exposure. At that speed, it’s going to be impossible to manage any sort of motion blur effect. However, with an ND filter – your camera sees the world as if it’s much darker outside. As a result, you can open up your shutter speed (or change other parameters). In this case, by creating a long shutter speed and using a tripod, we can actually get the water to blur – or the clouds to appear softer and in motion. See the before and after examples: 
You’ve likely seen photos of waterfalls or streams where the water appears to be a misty liquid flowing in a continuous stream. The secret? A Neutral Density filter – which can allow you to have, say, a one-second exposure on a bright sunny day. The true versatility of ND filters can be seen in the following table. It lists common ND filters and their respective transmittance values (source: Wikipedia). 
It’s inconvenient, however, to carry and change multiple ND filters. Now, with an adjustable ND filter, you can simply switch from ND2 to ND400 by spinning the ring. Just as an ND filter can improve things on the ground – so too can it provide some benefits for aerial photography. They are particularly useful in the following circumstances: - Improving Picture Quality (For Photography)
Aerial photography generally requires a well-lit environment. With a large fixed aperture, even with the ISO set to minimum (the minimum ISO value for the DJI Phantom 4 is 100), shutter speed will still be pretty fast. In this case, it often reaches 1/1000 or faster, which notably affects the picture quality. However, to obtain an optimal picture quality, the shutter speed of Phantom 4 camera should fall within the range of 1/80 to 1/150. This issue can be solved by simply mounting an ND filter to the camera. - Reducing Jello Effect (For Videography)
Even with vibration absorbers and gimbals, some drones transmit vibration to the camera. Though jello effect is fundamentally a result of vibration, shutter speed contributes significantly to the problem: The higher the shutter speed, the the greater the jello in the video. Using a Neutral Density filter allows the operator to decrease the shutter speed – and theoretically minimize or eliminate any jello. DJI has released specialized ND filters for its Phantom products. Pictured here is the ND16 filter on the Phantom 4. 
Phantom 4 Equipped with a ND Filter As you can see, accessories like ND filters can significantly add up to camera’s functions and improve user experience. Stay tuned – as even more accessories are just around the corner.
Source ： http://www.wetalkuav.com/neutral-density-an-awesome-addition/
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