B+W F-Pro Neutral Density filters main features
Extra-Slim Mounting Rings that Eliminate Problems Associated with SLR Wide-angle and Telephoto Imaging
The B+W standard filter mount F-Pro provides some substantial enhancements over the previous B+W standard mount. It has been given a shallower design while maintaining the excellent material and production quality and its unchanged high mechanical stability and can therefore now also be used without any risk of vignetting for many wide-angle lenses. While no exact focal length limit can be given, since the vignetting depends not only on the height of the filter mount, but also on the tube design of the lens, it can generally be considered that the B+W standard filter mount F-Pro can be used without any vignetting with 35 mm film, and indeed always up to 35 mm, almost always at 28 mm and frequently even at 24 mm focal length.
Another advantage of the new F-Pro mount is that the screw ring which holds the filter glass in the mount is no longer inserted from the front, but from the rear. This means that the screw ring can no longer be loosened unintentionally after an additional filter or a lens hood has been screwed on (too tightly) and then unscrewed again.