Antlia Herschel Wedge with 3 nm Calcium Filter for Solar Photography

Antlia 1.25" solar prism with complete equipment for photographing the sun in calcium light

The solar prism is suitable for refractor telescopes without built-in field flattener and is used instead of the star diagonal. About 96% of the solar energy is dissipated by the Herschel-type prism, the remaining 4 percent are available for photography. The images are sharper and richer in contrast than with simple objective lens solar filters. In addition, the image brightness can be continuously adjusted by means of an adjustment ring on the telescope-side opening. The housing is CNC-machined and has anti-reflective coatings to minimize contrast-reducing stray light.

The calcium filter with 3 nm bandwidth:

A narrow-band calcium (CaK II) filter is permanently installed. This filter allows solar photography in the calcium line at 393.3 nm. Sunspots are imaged in the calcium light similar to white light, but with more contrast. The flares, solar granulation, flares and even bright prominences in the edge region of the "solar disk" become visible to the photographer.

Important: Observations in CaK-II light are only useful photographically, because our eye can hardly or not at all perceive light of this wavelength. We suggest the use of a monochrome astro camera because it does not have a UV/IR block filter, i.e. it can be light sensitive up to the UV range. Also the Bayer filter of the color cameras darkens light noticeably below 400 nm.

Solar observation and photography with other telescopes

Basically, we recommend only refractors without built-in field flattening for solar observation. The heat of the sun would heat up a secondary mirror or corrector lenses too much. Damage would be very likely.

Herschel prisms must not be used on Petzval systems or other telescopes that have glass in the optical path near the focal point. Multi-lens systems do not pose a problem as long as all optics are only at the front of the objective.

More info about the Antlia Herschel prism:

The heat radiation is diverted into an extra thick polycrystalline ceramic diffuser plate. This prevents concentrated radiation. In addition, cooling vents above the ceramic plate facilitate efficient cooling of the system.

The 1.25" receptacle with the T2 connection allows the connection of cameras and eyepieces to the solar prism. On the bottom side, the receptacle offers an internal thread for mounted 1.25" filters, in which the 3 nm CaK II filter is firmly screwed in.

The 35 mm prism is coated with an anti-reflective (AR) layer on the back side to reduce stray light.