Herschelwedges (Solarprism) are made for the solar observation with refractors. Around 95% of the solar light will be blocked. With an variable polarising filter and strong grey filters the sunlight will be reduced to the necessary amount. Unlike objectiv solar filters the filtering happens close to the eyepiece or camera. Normaly the contrast and sharpness of the solar image with an Herschelwedge is much higher.