Baader Calcium K-Line Filter - 1.25" # CaK 2458355

Our Price: $357.00
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Our Product ID: OFIL-BP-CaK-1
Manufacturer SKU: 2458355
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Baader Calcium K-Line Filter - 1.25" # CaK 2458355

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  • Baader Calcium K-Line Filter - 1.25" # CaK 2458355

Please Note:  Because of the inclusion of the Baader astrosolar film with this filter, we do not accept any returns/exchanges for this item once it has been opened. All sales are final.

Quick Overview

  • Double stacked design allows high contrast imaging of solar granulation, flares, sunspots, and other solar features
  • Provides 8 nm wide bandpass at the Calcium II K-Line centered around 395nm
  • Works with your existing telescope – no need for expensive dedicated CaK modules or telescopes
  • Mounted in a standard 1.25” filter cell
  • Includes a 200mm X 290mm (8” X 11”) sheet of Baader AstroSolar Film (ND=3.8)

Product Details

Please note:  The Baader Ca K-Line filter is intended for imaging ONLY. It is not suitable for visual observation since the high UV levels can be an eye safety risk from prolonged observations. The CaK filter must be used in conjunction with a primary solar filter such as a Herschel Wedge Prism, or Baader AstroSolar Film (provided). The CaK filter must be placed after the primary filter (i.e. on the eyepiece), and cannot be used alone, or permanent eye and equipment damage will result. Also, due to the eye's low sensitivity and very poor resolving ability at 395nm, solar features in CaK are generally invisible for most observers.

The Baader Planetarium Double Stacked Calcium K-Line Filter makes imaging of the sun in the Calcium (Ca II) K-Line accessible to anyone with a telescope and digital camera or webcam. This double-stacked filter uses sophisticated coatings to produce a sharp 8 nanometer (nm) wide bandpass, centered at 395nm. This bandpass provides significant contrast for high-resolution imaging of granulation, flares, sunspots, and other features that are prominent in CaK light. The Baader K-Line filter works with your existing telescope eliminating the need to purchase a dedicated CaK telescope or expensive CaK modules - at a small fraction of the cost. The Baader CaK may be used with virtually any telescope, of any aperture - Newtonian, SCT, refractor, etc.

The Baader Double Stacked Ca K-Line Filter is enclosed in a standard 1.25" thread-on eyepiece cell. It can be attached to an eyepiece for projection imaging, or directly to a camera's nosepiece for prime-focus. The filter must be used with a solar pre-filter to reduce the heat energy that reaches the filter. A 200mm x 290mm (8x11inch) sheet of Baader's renowned AstroSolar Photo Film (ND=3.8) is provided with each Ca K-Line filter. This material may be easily mounted to any telescope using provided instructions.

The Baader Herschel Safety Wedge Solar Prism may also be used as the energy rejection filter in place of the AstroSolar Photo Film. This will provide the absolute highest quality solar images possible in CaK with the absolute least risk to eye or equipment damage.

As with all Baader Planetarium filters, the Solar Continuum possesses all of the trademark Baader filter qualities. Optical, physical, and mechanical qualities are superb.

Agena Note: Please note that this filter does not feature a female thread. Hence, you cannot stack additional 1.25" filters on to this item.

Useful Resources


Comparison between monochrome images taken with the Baader CaK filter (left) and the Baader Solar Continuum filter (right):


* Image Venus! *

In addition to imaging the sun in CaK, the Baader K-Line filter can be used to image Venus with some stunning results. The narrow bandpass of this filter enables imagers to record cloud structures of this bright planet, with results similar to the dedicated Baader Venus Filter. Image courtesy of M. Weigand.