There simply is no such lens. 12mm is extremely wide on full-frame and, if you are talking about rectilinear lenses, only Sigma ever made any. Their 12-24mm lens is now in its second version but is essentially the same lens. Going with a fisheye, there are still only two models, one from Sigma and one from Canon. Neither accepts filters.

The extreme angle-of-view of these lenses leave them with a protruding front-lens element which is sometimes protected by a minimal shade. Anything forward of that would cause vignetting which is why none of these lenses support any filters in front.

The Sigma 8mm F/3.5 fisheye however accepts gel filters at the rear of the lens as does the original Sigma 12-24mm but not the II version.

There simply is no such lens. 12mm is extremely wide on full-frame and, if you are talking about rectilinear lenses, only Sigma ever made any. Their 12-24mm lens is now in its second version but is essentially the same lens. Going with a fisheye, there are still only two models, one from Sigma and one from Canon. Neither accepts filters.

The extreme angle-of-view of these lenses leave them with a protruding front-lens element which is sometimes protected by a minimal shade. Anything forward of that would cause vignetting which is why none of these lenses support any filters in front.

The Canon 8-15mm and Sigma 8mm F/3.5 fisheye however accept gel filters at the rear of the lens as does the original Sigma 12-24mm but not the II version.