Baader 7.5 nm Solar Continuum 2" Filter, ZWL 540nm with 2" screw thread. A must-have for refractor owners: These filters narrow down the spectral range where a lens optic performs at its sharpest and most contrasted. The Baader Solar Continuum Filter enhances performance, increases contrast, and blocks atmospheric turbulence (when used in combination with white light solar filters). It provides a significant contrast gain in monochrome photography, even with color-accurate systems. Important note: The Baader Solar Continuum Filter should only be used for visual solar observation with additional filtration (e.g., Herschel prism or AstroSolar solar filter film).