Okay, I really think I'm being totally misunderstood. I was wondering if there is such a thing where the WHOLE piece of glass in a filter is polarized instead of half of the glass. I love to take photos of clouds. Not the whole sky, but a small portion of it and I don't want HALF the sky polarized and the other half not. Yes I am only an amateur but I just asked a very simple question that seems to have been misunderstood. I don't want a horizon line to worry about. Will a solid ND filter then give me a nice blue sky??
I've never heard of a split polarizer. There ARE split ND filters.
A solid ND filter will do nothing to darken the sky.... you would need to adjust the exposure accordingly and the sky will be rendered the same, just with a different set of exposure values (i.e., changing the shutter speed, aperture and/or ISO).
Solid ND filters do not rotate. They don't need to.
Split, or graduated filters, a required to rotate in order to 'line up' with the scene. They come in (the mostly useless) screw-in type,
And for the slide-in (Lee, Cokin, etc al):
Then there's the Variable ND filter, that must also rotate in order to adjust the density.
While ND and polarizers
look the same to us measely humans, they perform
vastly different functions when placed in front of a camera.