I'm flying a Mavic Pro 1 and shooting in 4K30. I know the best shutter speed for 30fps is 60. I am wondering if any multiple of 60 produces the same result. I have a limited supply of filters. ND8 ND16 and CPL by Polar Pro. I like the results I get with the CPL filer, but have to run a higher shutter speed to use it. Is this all just math or is there some magic to it that makes 60 better than 120, 240, 480 etc? I am having a hard time finding NDPL filters or sale for the Mavic Pro 1.
Thanks
You can of course set whatever shutter speed you want for any given framerate, but the reason you use 30fps and 1/60 is for a more "cinematic" look which, broadly speaking, produces motion blur most similar to what the human eye sees in day to day life.
Using too high of a shutter speed with a low frame rate makes motion very choppy - for example if you shot some ocean waves at 30fps with a 1/1000 shutter speed, the wave movement would look terrible (not smooth, very jittery).
Matching a higher shutter speed with a higher frame rate (eg. 120fps and 1/240 shutter speed) gives you the ability to capture motion extremely well, without any motion blur, and also the ability to produce buttery smooth slo-mo video down to 25% speed (or 4X slo-mo) assuming a 30fps timeline. This is why sports are often shot at 60fps. The trade off here is you lose the "cinematic" motion blur that the slower 1/60 shutter speed was giving you. It all just depends on what your desired outcome is, or what the intended end usage for the footage is. There is no real right or wrong answer as to what you
should be doing.
Unless shooting at higher frame rates (like 60fps or 120fps) you typically don't want to be raising your frame rate much higher than 1/60, but there is some leeway there - if you personally prefer, say, 1/50 or 1/80, or need to set it there to get the desired exposure, it's not going to have any significant negative impact on your footage. Flying very close to something or filming a fast moving subject will usually benefit from a slight increase in shutter speed even at 30fps to avoid excessive blur, but for general footage, 1/60 is a good place to be for 30fps.
The Mavic Pro 1 has an adjustable aperture though, so it should be quite easy for you to get away with the two ND filters that you have. You probably don't want to go much beyond F5.6 before diffraction starts degrading the image quite noticeably, but if you set your starting exposure for example at F4 and the ND8, changing the aperture to F2.8 or F5.6 effectively gives you a ND4 and ND16 respectively. Same deal if you were to set your exposure at F4 and ND16 - changing the aperture to F2.8 or F5.6 effectively gives you a ND8 and ND32 respectively. I hope that makes sense.
CPL filters cut about 1 stop of light, so that is one reason why your exposure changes, but since it's not a NDPL (a combination ND and CPL), it's only cutting one stop of light instead of several like your dedicated ND filters - that is why your shutter speed is much higher. The level of polarization also affects your exposure as the drone's angle to the sun changes. Due to the way CPLs work, your exposure
and the level of polarization change the moment your drone changes direction, even slightly. This makes CPLs extremely annoying to use on drones (assuming you want even footage), and you need a very specific pre-planned flight path to use them effectively. Regular CPLs are more suited for still image photography rather than video. If you want to shoot video with a CPL, you will probably want to get a ND/CPL combo filter and very carefully plan your flight path such that the level of polarization does not change during flight. With a drone, you do not have the same luxury as with a "regular" camera where all you have to do is reach forward and adjust the CPL on a lens - with a drone you have to return home and land just to make a slight adjustment to a CPL, which makes them incredibly annoying to use for many applications.