Polarizers, if you're shooting 90 degrees to the sun, will give you a darker blue in the sky. You can get some very nice rich skies that way. ND isn't going to do that for you. They work like sunglasses in that they lower the amount of light entering the camera, except the do this without changing the colors in any way.
Here's why it all works - and just skip this if you already know this...I'm not trying to be pedantic...but someone might want to know:
When you spin the exposure dial, you're changing the EV - which is YOUR REQUESTED exposure. You're effectively telling the Mavic how light or dark you want the image to be. From that point, the Mavic is going to do what it can to only let that amount of light hit the sensor. There are three things in play, the amount of light that's around, the size of the opening in the lens (called the Aperture), and the amount of time the sensor is exposed to the light (called the Shutter Speed). The Mavic has no control over how much light is out there, but it can control the other two (aperture and shutter speed). These two are inversely proportional, so if you double the length of time the sensor is exposed to the light, you need to halve the size of the opening in order to get the same exposure. Because of this, there are multiple "Correct" exposures. The Mavic, in Auto mode chooses both of these settings based common "normal" settings and tries to match the EV you set. That may be fine for a lot of people, but there are creative effects that can be had by choosing other balances between these.
On a plain Mavic with no accessories, the only thing we can set is the shutter speed (on other drones you can set both Speed and Aperture). The Mavic wants to expose the image to match the EV you requested. If you set the shutter speed, the Mavic will automatically set the aperture to be the right size to let in the amount of light to match your requested EV during the duration of the exposure. IF IT CAN. The problem that we face is that there is a maximum and minimum aperture size. If you pick a shutter speed that too fast, and the Mavic cannot open the aperture big enough to let in enough light, your picture will be underexposed and your shadow areas will black up. Conversely, if you decrease your shutter speed (like if you want water to blur a little), but the Mavic cannot close down the lens opening enough to limit the amount of light that gets in, too much light hits your sensor and your image will be overexposed and your light areas will wash out.
What an ND filter does for you, is control the third element of exposure...you're setting shutter speed, the Mavic is choosing the aperture...the third element is how much light is available. Normally, you're at the mercy of nature (how sunny is it?)...but with an ND filter, the amount of light that's available to the sensor is reduced...like wearing sunglasses. With less light to deal with, the Mavic can support slower shutter speeds within the limits of the aperture for a given exposure (EV). This lets you get creative by either choosing slower shutter speeds (which blurs and softens), or forcing shallower depth of field (the wider the opening of the lens, the less range that's in focus) by slowing your shutter speed and forcing the Mavic to choose a wider aperture to compensate.
So ND filters by themselves do not impact the image...but they allow the mavic to be set with slower shutter speeds, which does impact the image in both softness and depth of field.
Sorry if that's "TM already-known I" for most of the folks out there...Hope it's interesting to someone.
