Using ND filters correctly on GoPro cameras can make your FPV videos look more professional and cinematic by introducing the right amount of motion blur. I will explain what ND filters are and how to use them effectively to take your image quality to the next level.
What are ND Filters?
ND stands for “Neutral Density”, an ND filter reduces image exposure without changing the color of the image.
For cinematic FPV shots, we typically want to set shutter speed to a fixed value relative to the frame rate we are using, following something called “the 180-degree rule” (I will explain what it is shortly). This technique creates realistic motion blur and makes the video appears “more cinematic”. But when we do that, the image might be inevitably overexposed in a bright environment, and this is where ND filters come in (for reducing exposure).
Here’s a video comparing high shutter speed without ND filter, and lower shutter speed (fixed) with ND filter, the latter has more motion blur which gives the video a different feel.
Shutter Speed and Motion Blur
Before diving into what settings you should use on the GoPro, it’s useful to know the basics of photography if you are new to the topics.
There are 3 things that controls the exposure of an image:
- Shutter speed
Aperture is how much light you let in to the image sensor. As you lower Aperture, it lets more light in and the image will get brighter.
ISO is a digital gain applied to the brightness of an image. However it’s the last thing we want to use as increasing ISO also makes the image noisier.
Shutter speed is how long the camera opens the shutter for to let the light in. Digital cameras like the GoPro don’t have mechanical shutters, so the same term just means how long the image sensor samples the frame.
And shutter speed is what affects motion blur in our FPV videos. As you make shutter speed lower, the shutter is open for longer, the movements that happen within that frame will blur together, and this is motion blur.
Here is an example, from left the right, the shutter speed is lowered in steps and you can clearly see there’s more motion blur on the right. Lower shutter speed causes more motion blur, but requires a higher ND filter in order to keep exposure at the same level.
Mind you, too much motion blur is not always a good idea – it makes your video look out of focus. That’s why it’s important to know how much motion blur you need. It’s best to follow the 180-degree rules which I will explain below.
The 180-Degree Rule
The 180-degree rule is simple – for the number of frame rate, set your shutter speed to twice that number, e.g. for 30fps, set shutter speed to 1/60. This is referred to as shutter angle of 180 degrees, as to why, that’s outside of the scope of this post.
This rule should give you a good amount of motion blur. If you want even more motion blur, you can try shutter angle of 360 degrees (maximum limit), so the shutter speed is just 1 over the frame rate, e.g. at 30fps, set shutter speed to 1/30. But some people would consider this “too much motion blur”. You can also experiment with numbers between 180 and 360 degrees, but most people probably would be happy with just the 180 rule.
The same principle applies to high frame rate / slow motion shots, e.g. for 240fps, you want to increase shutter speed to get the same amount of motion blur e.g. to 1/480.
Why Use ND Filter?
Since shutter speed is fixed, you can only use Aperture and ISO to change image exposure. But GoPro doesn’t have Aperature setting, so that leaves us with only ISO which is the last thing we want to increase (because it makes the image noisy).
However, what tends to happen when shooting outdoor with a GoPro is that even when you set ISO to the lowest value (at 100), it’s still too bright and the image is over-exposed. This is when we can use ND filter to lower the amount of light entering the camera.
How to Use ND Filter?
I highly recommend using ND filters on your GoPro, not only it’s great for the video quality but also acts as a lens protector in the event of a crash.
ND filters come in different strength, ND2, ND4, ND8, ND16, ND32, 64 or even higher. The strength number indicates the amount of light reduction, a larger number means more reduction.
Your choice of ND filter depends heavily on the environment and lighting condition. This is what I personally use (30fps and 1/60 shutter speed):
- ND32 – Snowy day
- ND16 – Sunny day
- ND8 – Cloudy day, early morning and late afternoon in sunny condition
- ND2 and ND4: I rarely use them
- No ND – Just after sunset
It’s important to actually check your image exposure (preview) before shooting to avoid surprises.
Get your ND filters for the GoPro here. A set of ND32, ND16 and ND8 will get you pretty much all covered:
- Hero 11 and 11 mini: https://amzn.to/3VkEsiF
- Hero 9, 10, 11 and 11 mini: https://oscarliang.com/product-gm8h
- GoPro 8 – https://amzn.to/2MiJzxq
- GoPro 6 and 7 – https://amzn.to/2TUAKxU
Some ND filters allow to be stacked on top of another to increase the reduction, not always possible but good to know, for examples:
- ND2 + ND4 = ND8
- ND4 + ND4 = ND16
- ND4 + ND8 = ND32
Can ND Filters Remove Jello?
“Jello” is a phenomenon that appears when the camera is vibrating. Jello in FPV videos can be caused by many reasons, such as bad PID tune, beat-up frame/propellers, and faulty motor bearings.
In my experience, ND filters can reduce jello to some extend, but if there’s a lot of vibrations in your drone, instead of showing the up-down or left-right motion, ND filter blurs the movements together and everything would just look soft and out of focus. This property can be beneficial to FPV videos in some situations, but I would not use ND filter for the sole purpose of reducing jello. You should address the vibration issue in your drone when you have jello and not just “slap a Band-Aid on the root problem”.
- Apr 2018 – post created
- Dec 2022 – updated