In the world of videography there is a term which is quite often used, and that is the ‘180 degree shutter rule'. This 'rule' suggests that your shutter speed should be double your frame rate, so if you are shooting at 30 fps, then you should try and achieve a shutter speed of 1/60th of a second; allowing the viewers eyes to view motion in a natural manner and create a ‘cinematic look’ to your video.
One way this can be achieved is by closing down the aperture of the lens, however there are two factors which will have an affect on your ability to get the required shutter speed. The first is the aperture you may actually want to use, whether that be for artistic reasons or to get the required depth of field. If you want a shallow depth of field then you will need to use quite a large aperture of say f/2.8, which will also let more light through the lens to the sensor. The second is the available light you are working under, so once you have chosen the aperture you want to film with, the amount of light coming through the lens to the sensor may be too much, and you won’t be able to achieve the correct shutter speed for the frame rate you are working with.
So once you have chosen your frame rate, aperture, ISO and set the shutter speed to correctly expose the scene, only to find out that the shutter speed is too fast, what can you do? You can use a neutral density (ND) filter which allows you to decrease the amount of light getting through the lens by varying degrees.
A couple of months ago I received a DJI Mavic 2 Pro (M2P) drone for my birthday as I wanted to start creating video alongside my stills photography. The lens on the M2P has a variable aperture from f/2.8 to f/11 so you would think that you should be okay and be able to achieve the correct frame rate/shutter speed combination. Unfortunately this is not quite the case. An aperture of f/11 may not be small enough in bright sunshine. Also, doing tests with the different apertures of the M2P a conclusion is that sharpness starts to fall off after f/5.6, so you probably won’t want to go beyond that in the first place.
Basically I believe that to achieve a cinematic feel to the video from your drone you need to purchase some ND filters. Being a newcomer to the world of drones I didn’t know who made filters for my M2P, however after some research it seemed to be that one of the best manufactures out there is PolarPro. From here I headed over to the PolarPro website to see what filters they had for my drone.
PolarPro sell seven different packs of filters from their Cinema Series for the M2P, from the Exposure Collection which comes with three filters (7, 8 and 10 stop ND), through to the Cinematographers Collections which comes with 10 filters (2 - 5 stop ND and 2-5 stop ND/PL - polariser). In the end I decided to purchase their ‘6 Pack’ which as you would guess comes with six filters, comprising of 2, 3 and 4 stop ND filters and 2, 3 and 4 stop ND/PL filters. You can also purchase this set in two halves, the Shutter Collection being the ND’s and the Vivid Collections being the ND/PL’s. I chose the complete set as I knew I would most likely be filming over water or under blue skies at some point so the polarising filters would allow me to cut glare and deepen blue skies, and they also increase colour saturation a little.
Usually a sign of a good product is in the packaging, and the PolarPro filter packaging is very good indeed. A nice card box with quality printing and a magnetised cover on the front opens to reveal a plastic window showing the filters inside.
Inside The Packaging
Upon opening the box you will find a plastic tray which holds the plastic box containing the filters, a small plastic tool for removing filters from the drone (more on this later) and a small envelope contains a filter cloth, user guide, marketing material and a lifetime warranty card.
The Filter Box
The box containing the filters is very well made with a strong plastic, and has a hinge opening and magnetic closure. Unfortunately though, the fact that PolarPro have decided to use magnets to keep box shut could be problematic. This is because magnets being close to your drone can cause problems with its compass, so a good idea would be to make sure that when installing or changing filters that the box is a reasonable distance away from your drone. The filters themselves are held in place nicely, can be removed easily and should not move around in transit.
On the image below you will see the ND filters on the left and the ND/PL filters on the right. The ND/PL filters are the circular polariser type which you rotate to get the desired amount of polarisation.
The filters are made from aircraft aluminium, with glass which is said to have a low refractive index, colour neutrality and perfect target transmission (taken from the PolarPro website), so you would expect these to be of a very high quality. The ND/PL filters have markers which indicate the point at which the polarisation is at its strongest. When I am using my DSLR with a polarising filter in place and where there is blue sky in my composition, I very rarely rotate the filter to its maximum polarisation, as this can make the sky too deep a blue which looks unnatural. Therefore I would guess with these filters that I will either set the polariser manually or line the markers up and go a little further beyond.
Installing The Filters
The removal of the stock UV filter which comes with the M2P is removed pretty easily by holding on to the camera firmly with one hand and with the other hand, rotating the UV filter counter clockwise. Some people find this hard to do, so PolarPro have designed a plastic tool which helps to make this process easier. In all honesty I have been able to remove all the filters from my M2P camera with ease. Putting a new filter in place is pretty straight forward as well. You simply need to make sure the filter is the right way up (for the ND’s this means making sure the PolarPro logo is to the top, and for the ND/PL’s there are markers on the underside showing which way is up), marry up the pins on the filter with the holes on the front of the camera and rotate clockwise.
If in doubt here is a link to a video on YouTube from PolarPro, showing you exactly how to do it How to Install Mavic 2 Filters (Pro & Zoom).
To test the filters in the field I headed out one afternoon where there was blue sky with some high cirrus clouds. I took seven images, starting with the stock UV filter in place, sent the drone around 15 metres up into the air, took a photo, landed the drone, changed the filter then repeated until I had taken a photo with all six PolarPro filters.
With regards camera settings, I set the white balance to sunny (as it was), set the aperture to f/5.6, then set the appropriate shutter speed based on getting the histogram to be as close as possible for each image. For the ND/PL filters before taking off I would point the drone in the direction to where I would be taking the photo and rotate it until I saw the polarisation I wanted.
Below is a slideshow containing the seven images I took to test the various filters (click on the thumbnails below to view the larger image).
Unfortunately the sun disappeared behind cloud a couple of times so I wasn’t able to fully test whether the filters really do block the light by 2, 3 and 4 stops. However, based on the shutter speeds set at the time I would say that they are what they are supposed to be, if not very close.
The clarity is excellent with no signs of any degradation compared to the image using the stock UV filter from DJI. The polariser filters certainly do what they are supposed to as you can see more detail in the sky with regards the cirrus clouds. They also have a slight warming effect which I personally quite like as my regular photography polariser does the same.
Although these are the first drone filters I have tried they will most likely be my last as I don’t see any issues with them.
The PolarPro filters for which I use on my DJI Mavic 2 Pro can be purchased here on Amazon.