Astro-Physics is pleased to offer the Baader Planetarium’s 2" Cool-Ceramic Safety Herschel Prism. This Herschel prism affords the finest detail possible in solar viewing. The contrast and sharpness that it provides when observing surface detail will leave you breathless. No solar filter can compare! Additionally, it reveals the sun in a true white-light, uncolored by filters.
A Herschel prism is a unique prism that is angled at 23 degrees. It passes 95.4% of the sun’s light and heat through the prism and out the back side. The 4.6% of the light that is directed to the eyepiece requires the use of a 3.0 neutral density filter. This filter must always be used when visually observing and, therefore, is permanently installed.
This new generation Herschel Prism incorporates some unique features that add to its safety and ease of use. A layered, perforated-metal heat cage traps the excess energy transmitted through the prism, rendering it harmless. What little light and heat that remains is finally absorbed by a translucent ceramic tile. This translucent tile displays the image of the sun, serving as a solar finder. Simply move your telescope about until you see the sun appear on the translucent tile and you are all set. It is much quicker and more accurate than watching the scope's shadow on the ground.
We are offering the “photographic version" of the Baader Herschel Prism. This version comes complete with a full compliment of 2" neutral density filters (ND-1.8, ND-0.9, ND-0.6 and permanently mounted ND-3.0) and a 2" Solar Continuum filter. The Solar Continuum filter helps to further boost contrast, revealing sunspot and surface granularity detail (it does have a green colorization). A foam-lined metal carry case is provided for convenience and protection. The Baader Herschel Prism is compatible with Baader's Astro T-2 System. Please follow this link to view a copy of the manual.
Note: Baader lists the light path distance as being 114 mm measured from the nosepiece flange (not the insertion depth) to the top flange of the eyepiece holder. The position of eyepiece optical centers will reduce this spacing by 5 to 10 mm since the eyepiece will sit down into the eyepiece holder. When using the Herschel Prism for imaging, the eyepiece holder can be replaced with the Baader 2" to 42 mm adapter (BP27) so that a camera can be directly attached using a camera T-ring. This configuration will have a spacing distance of 67 mm flange to flange, plus the T-ring and camera. Please see the above link to the Baader manual for more information.
A question that is always asked is, "Does it damage my telescope to have it looking at the sun for long periods of time?" No! The lens passes the infrared (heat) part of the spectrum as efficiently as the visible part of the spectrum. Since the lens does not absorb or retain the infrared light, it does not heat up.
CAUTION - Important Limitation of Use: It is important to know that a Herschel Prism can only be used with refracting telescopes. It can not be used on any style reflecting telescope. If you own a Petzval-style refractor, or any design which puts elements to the rear of the scope where excessive heat build-up can occur, it is best to check with the manufacturer regarding their specific scope. [Note that Al Nagler of TeleVue has stated that the rear elements of the TeleVue Petzval scopes are sufficiently forward that no damage will occur to their scopes.] Regarding visual use, Baader has tested the prism for safety in refractors up to 8" apertures. They do note that you will want to add an additional neutral density filter for viewing comfort with the larger scopes.
CAUTION - Secondary optics, such as flatteners, telecompressors, barlows, and filters need to be placed after the Herschel Prism, not in front of it.