A common question is:
“Why do I need an 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 stands for Neutral Density which means that even though less light is transmitted through the glass, colors are not affected at all and can be manipulated color correction in post.
We listed best ND Filters 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 sometimes becomes visible and it creates an extremely sharp image which looks unprofessional because the viewer tries to focus on everything in your video instead of the main subject.
To avoid this, we aid our little camera sensor by adding an ND (Neutral Density) filter.
They reduce the amount of light that enters the lens and that way camera doesn’t need to bump up the shutter speed and you are more flexible to tweak the exposure.
Additionally, lower shutter speed creates a motion blur. We see motion blur every day with our own eyes. Our brain blurs out a lot of things we see with our eyes in order to focus on something else.
Same goes for 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 ND filters reduce it?
A lot of camera drones have small sensors and they also have fixed aperture as we stated earlier, so to maintain the correct exposure you need to alter either one of these 2 things:
- The ISO (sensitivity of the sensor)
- The exposure time.
At ISO 100 a bright day may still be too much for the sensor when calculating exposure making a picture too bright, so the only option for the camera’s sensor is to decrease the exposure time. (1/250 of a second has twice the exposure of 1/500 of a second so 1/500 will be 2x darker).
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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 (i.e. top to bottom or side to side). The problem with these cameras is that it takes time for a sensor to “read” whats happening. And for that small amount of time that it needs to scan from one side to the other, subject that you are shooting has moved a little bit.
To start scaning the next frame, the subject has moved a little bit more so the image looks disjointed. This looks particularly spectacular if the target object is also moving fast (like a propeller). It creates a really weird rolling shutter effect.
And the other thing that makes this worse is vibration, as it is a small rapid movement of the camera. Imagine if you were standing on a vibrating surface… Your vision would most certainly be blurred.
So to fix the rolling shutter you have to:
- Minimise vibratory movement (gimbal)
- Slow down the shutter speed (with the ND filter).
It produces an image that is not completely frozen in time, but it is somewhat how your eyes perceive movement. 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.
Here are some videos that will shed more light onnto this topic:
We hope this helped you.
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