A common question is:
“Why do I need a ND filter for my drone?”
Neutral Density (ND) is a type of filter that you will find in every pro photographers’ kit. It reduces the amount of light that comes through the lens. Basically like sunglasses. Every filter is marked by a number. The higher the number, the bigger light reduction is. Which means less light comes to the sensor.
Most Drones have fixed aperture with Shutter Speed and ISO being only variables available to set a correct exposure. And the problem is that drones fly very high, and there is a lot of light up there. But don’t worry, *ND filters* are here to help!
The ND as stated standard for neutral density which means that even though the light transmitted through the glass is less the colours are not affected and can be manipulated by colour correction as per normal.
We listed the best ND Filter for your drone below
Why is a lower shutter speed better?
As we said before… Drone Camera has fixed aperture, which means it can control the exposure only by ISO and shutter speed. If the light is too bright, camera increases shutter speed (less light comes to the sensor) and that way it compensates for the lack of ND filter…
But the problem with high shutter speed is that the jello effect becomes visible and it creates a distorted image which looks very unprofessional. To avoid this, we help the camera by adding an ND (Neutral Density) filter. They reduce the light and that way camera doesn’t need to bump up the shutter speed and you have more space to tweak the exposure.
Additionally, lower shutter speed creates a motion blur. Motion blur we see every day with our own eyes. Our brain blurs out all the information we see with our eyes in order to focus on something.
Same is in your video footage… if everything is sharp with no motion blur, it doesn’t seem natural and is not easy on the eyes
Jello (Rolling Shutter effect) and why NDs reduce it.
Because the small sensors on the cameras are fixed aperture as we stated. So to maintain the correct exposure you need to alter either
a) the ISO (sensitivity of the sensor) or b) the exposure time.
At ISO 100 a bright day still may be too much for the sensor in exposure making it a white out so the only option for the camera’s sensor is to decrease the exposure time.
So 1/250 of a second has twice the exposure of 1/500 of a second (all other things considered).
We explained the optimal camera settings for the Phantom 3 and Mavic Pro in seperate article, more model will follow up soon. Click here for the Mavic Camera Settings.
And here for the Phantom 3 Camera Settings.
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Now back to the camera.
If the camera is taking a single shot in 1/1000 of a second then it has to capture all the information quickly.
The camera does this in a scanning pattern (ie top to bottom or side to side). When it does this it makes for a very ‘still’ image. Think clear picture of a person kicking a ball where everything looks completely frozen in time.
The problem with the cameras is that it is moving at the same time and by the time the scan is getting to the bottom of the sensor to start again the image has moved so the still image looks disjointed. This looks particularly spectacular if the target object is also moving fast (like a propeller) Propellers showing rolling shutter effect.
And the other thing that makes this worse is vibration as it is a rapid movement of the camera (I have personal experience of this with 2 GoPros strapped directly to a Harley Davidson….not fast but very buzzy and lots of Jello!).
So to fix the rolling shutter you have to a) minimise vibratory movement (gimble) and slow down the shutter speed (with the ND filter). It gives an image that is not as frozen in time but it is somewhat how your eyes perceive movement anyway. You see the motion as normal and it is not frame shifted due to the length of the exposure allowing the whole image to hit the sensor in a more natural fashion.
When do I need which ND Filter?
Note: With a Set of PL , ND4 and ND8 Filter (If you live in a sunny state +ND16) you are prepared for 98% of all situations.