The APM Herschel wegde offers a really good performance for a very reasonable price.
Herschel wedges (Solar prisms) are made for the solar observation with refractors. Approx. 95% of the incoming solar light will be blocked. With a variable polarizing filter or strong neutral density filters, the sunlight can be reduced to an usable amount. Unlike objective solar filters, the filtering happens close to the eyepiece or camera. Normally the resulting contrast and sharpness of the image will be qualitative better with a Herschel wedge. The full solar energy enters the telescope and the filtering happens close to the focal plane, so we only recommend refractors for the work with a Herschel wedge. And important, the refractor shouldn't have a rear corrector lens. The optical elements would heated up through the concentrated energy and could be damaged. Also filters are only allowed at the eyepiece side of the Herschel wedge and not at the front side.
Additional to a better image quality, the Herschel wedge offers more light. So you can use special contrast filters, like the Baader Solar Continuum. With filters like these you can increase the contrast of the sun image. Of course 5% are too much for visual solar observation. So, you need an additional filter for light reduction. A neutral density 3 filter is screwed directly in the prism body. Because the Herschel wedge produces polarized light, you use the internal polarizing filter for additional light reduction. Now you can rotate the eyepiece sleeve and so reduce the light level.
This Herschel wedge comes with integrated ND3 density filter and polarizing filter.
