Baader Calcium GEN-II 1.25″ Filter with Low Profile Filter Cell (LPFC)

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AstroSolar Photo Film OD 3.8 Add to Basket:----------Choose:  20cm x 29cm:  + £27.00

Steve Ringwood writing for Astronomy Now Magazine

"Athough the Sun graces the sky all through the year (clouds permitting), it is fair to say that the warmer weather in the summer months brings out the latent solar observer in all of us. White-light solar filters and Herschel wedges give us access to the photosphere, while hydrogen-alpha narrowband methodologies let us see the incredible drama of the chromosphere. However, there is another window on the Sun's activity, that of the violet calcium-K line, at 393.4nm.

Baader's new GEN-II calcium-k filter features a 1.25-inch filter that passes the 393.4m wavelength within a narrow window of just 5m.

It replaces a previous version with a wider bracket of 8nm, meaning that the GEN-II does not need to be stacked to achieve the same precision. Use of this filter must be teamed up with Baader's AstroSolar Photo Film OD 3.8, from which you build your own full aperture filter. 

The GEN-II features Baader's new and thinner LPFC (Low Profile Filter Cell) mounts and therefore is more versatile on the deployment front."  

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Baader Calcium GEN-II 1.25″ Filter with Low Profile Filter Cell (LPFC)

IMPORTANT: Never use this filter for visual observations, as our eye is blind for the harmful UV-radiation, but can be damaged by it.

The new Baader Calcium GEN-II filter lets you observe the interesting border region between the photosphere, visible in white light, and the sun's chromosphere, 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 and 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!

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 optimised for best sharpness in this part of the spectrum). Nevertheless, many lens telescopes still work well 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 package is a sheet of AstroSolar Photo Film OD 3.8, 20×30 cm (#2459278 ) to build a solar filter by yourself to 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 (already in the scope of delivery of the Baader Safety CoolCeramic Herschel Prism 2″ Photographic (#2956510P).

The calcium GEN-II replaces the older K-Line Filter 1¼” (stacked) # 2458355. Thanks to modern manufacturing techniques, a single filter achieves better quality and narrower half-band width (FWHM) of only 5 nm instead of the previous two filters'  8 nm; stacking is 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.

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

• Increased contrast, matched for typical CMOS quantum efficiency and s/n ratio
• Reflex-Blocker™ coatings, for the 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 is coated individually, with a 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-ageing coating for life – even in a most adverse environment

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