I can see a matte box in my future. For handycams or possibly a smaller shoulder mount sized cams, are 4x4 filters large enough, or is the 4x5.6 needed.
If you have a lens with a 77mm front this gives you about 11mm per side to play with, actually less because the filter holder may take up a couple of mm and even less if you intend to stack multiple filters with a gap between them.
If you imagine a lens collecting a cone of light you will see that at if the filter is far from the lens, or the cone of light going in to the lens is wide (angle) then the cone will intersect the 4X4 square - vignette
As a guide from experience I would say that 18mm at S35 chip with a 77mm front element is about the maximum appropriate* projection for a 4X4 filter, 2 filters max. Lenses, including the canon 16-35, or anything larger or wider, would be collecting a projection cone large enough to certainly require a 5.6 filter (when shooting an S35 chip).
S
*aka challenging and requiring careful selection and placement of MB
