: PENFLEX FILTERS PF-CPL77 CPL Filter 77mm, Black : Electronics. The front ring of the Polarizer rotates and may be adjusted for maximum effect . Thin Metal Ring will Not Vignette . Optical glass for maximum sharpness and light transmission . Penflex Circular Polarizers (CPL) are manufactured from Glass with Polarizing materials incorporated. The rings are metal and feature a male thread which screws into the filter, and a female thread on front to accept lens hoods, other filters or accessories. Once attached to a lens, the front ring of the polarizer rotates and may be adjusted for maximum effect. This is typically done by looking through the viewfinder while turning the front ring on the filter. Slim Design. Designed with a slim design metal ring. The thickness of the metal ring projects only 6.5 mm past the front of the lens. Knurled front edges provide a better grip. Total thickness of the filter is only 8.2 mm . . .