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APM 2″ Herschel Wedge
The operation of the APM Herschel 2 inch wedge (also called Herschel prism) is based on the principle that only a small part (about 5%) passes through. The 95% larger and also more energy-rich part, is passed through the housing. This forms a focal point outside the prism, even far behind this focal point. The light concentration is still very intense. Users (with older prisms) had to exercise caution, so that no inexperienced observer accidentally looks into the output light beam.
The APM 2 inch Herschel wedge is equipped with the ceramic light trap. This is made up of a multi-coated integrated ND3 filter and (replaceable) polarizing filter. This arrangement makes sun observation with a Herschel wedge a safe bet.
The image brightness can be regulated by rotating the polarizer. Thus, the Herschel Wedge is both visually and photographically perfect!
The Clear Aperture is 46mm!
The use of the Herschel prism (in comparison with film filters) for solar observation is that it is not only safer, but also performs to a higher quality. The generated image is rich in contrast and sharp in focus and can be used for high magnification.
Important note: The application of the Herschel prism is only suitable for refractors and mirror based systems.