Herschel wedges (Solarprisms) are made for solar observation with refractors. Around 95% of the solar light is be blocked. Using a variable polarising filter and neutral density filter the sunlight will be reduced to a necessary amount for safe use. Unlike objective solar filters, the filtering happens close to the eyepiece or camera. This results in much higher contrast and sharpness of the solar image.
The advantages of the APM / Lunt Herschel Wedge:
· Perfect surfaces for very high contrast
· Completely enclosed housing with integrated heat trap
· No scattered light escapes for maximum safety
· Delivered in aluminium case with foam insert
· Supplied with pre fitted Baader ND3 neutral density filter
· Supplied with Baader Solar Continuum filter for high contrast observing and imaging
Only for use with refractors!
The full solar energy enters the telescope and the filtering happens close to the focal plane. Therefore only refractors should be used.
Use with a Reflector will result in over heating and potential explosive destruction of the secondary mirror!.
The refractor type used should also not have have a rear corrector lens. The optical elements will be heated through the concentrated solar energy and could be damaged. Also filters are only allowed at the eyepiece side of the Herschel Wedge and not before it.
The advantages of using a Herschel Wedge with refractors:
In addition to the better image quality, the Herschel Wedge provides more light. This allows use of a special contrast filter, like the Baader Solar Continuum. With filters like this you can increase the contrast of features on the Sun. Note a Solar Continuum filter is best used if you have an Achromatic refractor as it will not show false colour. For Apo’s we recommend using a Polorising filter which also enhances contrast and also allows you to adjust brightness by rotating the eyepiece in the wedge.
