The Tiffen 125mm Coarse Thread Digital Diffusion/FX 4 Filter is a softening and diffusion filter specifically meant to appear invisible, as if no filtration is being applied. Compared to other diffusion filters, this filter offers virtually no flare or loss of contrast for more subtle applications. It helps to lessen facial blemishes, wrinkles, and gently smooth textured backgrounds while maintaining sharp focus. The 4 density provides more softening than the 3, but less than the 5.
This filter is constructed from Water White glass and is made using ColorCore technology, a process that involves laminating the filter substrate between 2 pieces of optical glass, grinding flat to a tolerance of 1/10,000th of an inch, and then mounting to precision metal rings.