Calcium GEN-II Filter 1¼" (incl. AstroSolar Photo Film OD 3.8, A4)

Calcium GEN-II Filter 1¼"

The calcium GEN-II filter lets you observe the interesting border region between the photosphere, which is visible in white light, and the chromosphere of the sun, which is reserved for narrow-band H-alpha filters. In addition to the structures known from white light, such as sunspots, you can see the chromospheric network distributed over the entire surface of the sun, which precedes the formation of sunspots, as well as cells of supergranulation and Ellerman Bombs.

The emission line of calcium at 394 nm is already in the near UV. That's why observing the sun at this wavelength is only possible with a camera! Never use this filter for visual observations, as our eye is blind for the harmful UV-radiation, but can be damaged by it.

This filter delivers the best results when used with a monochrome camera (which is more sensitive in this part of the spectrum than a colour camera) and mirror telescopes (because especially refractors with fast f/ratios are not optimized for best sharpness in this part of the spectrum). Nevertheless, many lens telescopes still work fine for calcium observations; unmodified DSLRs may need extremely long exposure times.

All calcium-filters require an additional solar filter in front of them. Part of the Baader GEN-II is a sheet of  AstroSolar® Photo Film OD 3.8, 20x29 cm - not for visual observation (#2459278 , € 34,- )  to build a solar filter by yourself, so that you can start observing without purchasing any other filters. Of course, you can also use one of the BDSF: Baader Digital Solar Filter OD 3.8 (80mm - 280mm) which are already mounted in a filter cell. On suitable lens telescopes, you can also use a Herschel prism. That way, you can replace the integrated ND3-filter mounted behind the Herschel with a weaker filter to reach shorter exposure times. These filters are already in the scope of delivery of the Cool-Ceramic Safety Herschel Prism 2" Mark II – Photographic (#2956510P , € 645,- ) .

The calcium GEN-II replaces the older K-Line Filter 1¼" (stacked) # 2458355. Thanks to modern manufacturing techniques, a single filter now achieves a better quality and narrower half-band width (FWHM) of only 5 nm instead of the previous 8 nm; stacking two filters is now no longer necessary. This also makes it possible to use the filter in standard filter wheels/drawers; the low-profile filter mount is only 6 mm high when screwed in.

Baader Calcium GEN-II at ED 80/600

Baader Calcium GEN-II at 80/910 Fraunhofer

To use the 1¼"-filter at cameras with 2"-nosepiece, you can use either use a filter drawer like the Baader UFC System or a filter wheel. You can always use the filter thread of many barlow lenses as well as 1¼" nose pieces like 1¼" Nosepiece to T-2a – with Safety-Kerf (#2458106 , € 31,- ) . You can mount it between two parts with T-2-threads by combining 1¼" Filter holder T-2a to T-2a – with 1¼" filter thread (#1508030 , € 33,- ) and  Inverter ring T-2i (male to female) (#2958110 , € 29,- ) ; for cameras with a 2" filter thread, you also need Adapter M48a to T-2i (#2458110 , € 22,- ) .

You can find a first review here:

First Impression of the new Baader Calcium Filter

The Baader Calcium GEN-II has got all the advantages of the new generation of CMOS-optimized Baader filters:

• Increased contrast, matched for typical CMOS quantum efficiency and s/n ratio
• Reflex-Blocker^™ coatings, for largest ever freedom from halos, even under most adverse conditions concerning aux-optics
• Identical filter thickness to existing standards, with utmost care for parfocality
• Blackened edges all around, with filter-lead-side-indicator in the form of a telescope-sided black outer rim, to additionally eliminate any reflection due to light falling onto the edge of a filter
• Each filter coated individually, with sealed coating edge (NOT cut out of a larger plate with coatings left exposed, read more)
• Life-Coat™: evermore hard coatings to enable a non-aging coating for life – even in a most adverse environment