The Generation II Baader K-Line filter is designed for photographic solar imaging of the Calcium K- and H-lines and must be used with the included AstroSolar OD 3.8 film.

This second generation version of the filter has a narrower half-bandwidth of 5nm centred around 394nm and newly designed coatings which makes photography of the boundary layer between photosphere and chromosphere possible. As the human eye is damaged at these wavelengths, the Baader K-line filter is not suitable for visual observation.

Unlike the previous version, this is not a double-stacked filter as the newly developed coatings make this unnecessary. Additionally, the filter now comes in Baader's standard low profile filter cell for maximum compatibility with common equipment.

The Calcium-K filter is best used with a monochrome camera and mirror telescopes (as refractors are not optimized for sharpness at this end of the spectrum). However, many longer focal ratio refractors still provide good images and unmodified DSLRs can be used (albeit with very long exposure times).

Calcium-K light is emitted from a layer about 500km above the photosphere, where the boundary between the upper photosphere and lower chromosphere lies. Here the solar disk appears deep blue, with a bright network of structures revealed. These so-called "plagues" are associated with faculae and sunspots and can be seen all over the sun. Occasionally one may capture Ellerman bombs - micro-flares close to sunspots.

WARNING: this filter is only to be used for photographic observation, not visual! Our eyes are easily damaged at these UV wavelengths. All calcium filters require an additional neutral density filter in front of them, such as the included Astrosolar Photo film. Baader's Herschel Prism can also be used with suitable refractors.

All Baader filters (excluding 100 x 100mm) come in stackable labelled filter boxes which can be attached to each other to form a sturdy filter library.

$Baader Calcium K-like Gen II filter example with ED80 refractor$

Example of Calcium GEN-II filter with ED80 refractor at 600mm.

$Baader Calcium K-like Gen II filter example with Vixen 80mm f/11 refractor$

Example of Calcium GEN-II filter with Fraunhofer 80mm f/11 at 910mm.

Specifications

Transmission range	CaK-II
Half-bandwidth	5 nm
Central wavelength	394 nm
AR-coating	Dielectrically coated, planeoptically polished
Filter thickness	2 mm (6 mm with cell)
Filter size	1.25" mounted
SKU	BA2961590

Downloads

Review of the Calcium GEN-II filter

SOLAR FILTERS