Antlia Herschel prism for solar photography and observation.

Antlia 1.25" Solar Prism

The solar prism is suitable for refractor telescopes without built-in field flattening and is used instead of the star diagonal. About 96 % of the solar energy is diverted by the Herschel-type prism, the remaining 4 % are available for photography. The images are sharper and richer in contrast than with simple front lens sun 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 minimise contrast-reducing stray light.

Adjustment of image brightness

For observing the sun, 4 % transmission is of course too much. You definitely need light attenuation filters. An ND3 filter is screwed into the eyepiece sleeve. Since the Herschel prism polarises the light, a simple polarising filter screwed into the eyepiece or photo adapter is sufficient to further reduce the brightness. Turning it reduces the brightness. With grey filters and the Baader Solar Continuum Filter, you can further reduce the brightness to the desired level and influence the contrast.

Warning!
Never use the Herschel prism without an ND3 and additional polarising or Solar Continuum filter!!! Otherwise there is a risk of irreparable eye damage!!!

Sun observation and photography with other telescopes

Basically, we recommend only refractors without built-in field flattening for sun observation with Herschel prisms. The heat of the sun would heat up the 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 on the Antlia Herschel prism:

The heat radiation is dissipated 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 underside, the receptacle offers an internal thread for mounted 1.25" filters, into which a 3 nm CaK II filter can be screwed.

The 35 mm prism has an anti-reflective (AR) coating on the back side to reduce stray light.