The Antlia Solar Discover CaK 5Å solar filter is designed to optimize the contrast of images of plages, faculae, sunspots and other visible features in Calcium K (CaK) light at 393.3 nm using very narrow bandpass filters.

This 5Å Antlia ultra-narrow bandpass filter has an aperture of 12 mm and a wavelength centered on the Calcium K line at 393.3 nm. With its ultra narrow bandwidth (FWHM) of 5Å, it enables the capture of chromosphere details.

The filter body is made of aircraft aluminum, machined from billet and machined with high-precision numerically controlled (CNC) machines.

Designed to work at the focus of a refracting telescope with a focal ratio of at least F/7, dedicated 2x, 3x and 5x Barlow lenses are available and can also be purchased preinstalled (see variants) with the filter itself.

If the telescope has a built-in corrector near the focus, a rejection filter (ERF) is required to be placed in front of the objective. For refractors with a classic doublet or triplet scheme, up to 100 mm the ERF built into the Solar Discover is sufficient. If using a mirror diagonal, we recommend an additional ERF in a 2" filter holder cell, sold separately and to be placed before the diagonal. The use of prism diagonals is not recommended. For apertures larger than 100 mm, a full-aperture rejection filter is required, or the lens must be diaphragmed.

Please note: Any additional ERFs must allow the H-calcium lines @ 396.8 nm and K-calcium @ 393.3 nm to pass through, in addition to the H-alpha line @ 656.3 nm. The optional rejection filters offered by Antlia Filter meet these requirements.

CaK 5Å version equipped with double barrel for 2" / 50.8 mm and 1.25" / 31.8 mm eyepiece holders.

Visual Observation

Unfortunately, the Calcium K line (393.3 nm) is almost invisible to the human eye, so the Antlia Solar Discover CaK 5Å solar filter is mainly used for solar imaging and is not recommended for visual observation.

Please note that the infrared filtering of these Antlia Solar Discover solar filters differs slightly from the ISO 12312-2 standard for solar viewers. See the table below and refer to the ISO 12312-2 standard for solar viewers (https://eclipse.aas.org/eye-safety/iso12312-2).

ISO12312-2 Transmission Requirements Antlia
Requirements Value
Range of Wave Lengths Range of Wave Lengths.
Tmax% 0.0032%
Tmin% 0.000061%
Tmax% (UVB) 0.0032%
Tmax% (UVA) 0.0032%
Tmax% (IR) 3%

Due to strict technical requirements and safety considerations, we do not recommend the use of these filters for visual observation. If you wish to use the product for visual observation, it is essential to ensure that all integrated filters are in perfect condition. For more information, please contact us directly.

Scope of Delivery:

• Filter-only version, with integrated Barlow lens (2x, 3x or 5x)