ND filters are one of the most useful accessories both stills and video shooters can own. They come in two fundamental variants (fixed and variable), and this helpful video will help you decide which is right for you.
Coming to you from ZY Productions, this great video talks about the pros and cons of fixed and variable ND (neutral density) filters. ND filters work to reduce the amount of light entering your lens and are highly useful for both photo and video shooters. For stills, they can be used to achieve a longer shutter speed, allowing you to employ creative effects like long exposures of flowing water. They can also be used for shooting outside at wider apertures when using a flash that doesn't have high speed sync. For video shooters, you can use an ND filter to dial in the correct shutter speed for a given frame rate that will allow you to follow the 180-degree shutter rule. Whereas fixed ND filters cut the light by a constant amount, you can adjust the power of a variable ND filter, but that convenience is not without drawbacks. Check out the video above to help decide which is right for you.
Should we shoot with primes or zoom lenses?
You should put a variable ND on your zooms and a fixed ND on your primes. ;-)
Variable ND in my opinion is a terrible invention and the color cast and even vignetting is usually too much over.
Even circular ND filters (any) is a huge issue as after you focus without the filter the huge chace you will mov focus (either the ring or the camera or both) when mounting the filter ... I would always go only with square glass system filters ... it makes things much easier - you need different one or more .. .just attach ...
I can't say that I've ever run into this particular issue. Perhaps it's more of a problem on zoom lenses than primes?
I prefer just normal ND filters because it means less additional glass in the optical path.
I don't own a variable ND filter, but I own and use the regular type. I use Hoya thread on filters as I've found they give no color cast. My go to lens is a Canon 16-35 f4L which makes a good combination with the filters.