Why can't I use the Antlia CaK 3nm filter for visual solar observing?
The filter transmits light at the 393.3nm wavelength, which is in the deep violet part of the spectrum. The human eye has very poor sensitivity and resolving ability at this frequency, making solar features nearly invisible. The filter is designed for imaging with cameras that have spectral responses well beyond human vision. Never look into the Sun with the K-line filter alone: although you don't perceive it, a lot of harmful UV radiation enters your eye.
What solar features will the Antlia CaK 393.3nm filter show me?
Antlia designs the CaK filter to maximize contrast for high-resolution imaging of features prominent in CaK light. With a camera, you can image:
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Sunspots: Named by Antlia as a target.
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Granulation: The "cell-like" texture of the solar surface, named by Antlia.
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Plage: Bright, active regions that often surround sunspot groups.
Do I need the Antlia CaK filter if I own the Antlia Herschel Wedge?
No. This CaK 3nm 393.3nm filter is screwed into the Antlia Herschel Wedge prism, so you do not need to buy it separately if you use the Antlia Herschel Wedge.
What kind of telescope do I need to use the Antlia CaK 3nm filter?
Antlia presents this filter only as the internal CaK filter that screws into the Antlia Herschel Wedge prism, and it does not list other telescopes or solar filters for it. It is not a stand-alone solar filter and is for imaging only. Never look into the Sun with the K-line filter alone: although you don't perceive it, a lot of harmful UV radiation enters your eye. Contact us before planning any other setup.
Can I image sunspot groups and active regions with the Antlia CaK filter?
Yes. Antlia designs the 3nm bandpass to maximize contrast for high-resolution imaging of sunspots, solar surface granulation and other features prominent in CaK light, such as the bright plage around active regions. Results depend on your optics, camera and seeing.
Can I stack the 1.25" Antlia CaK filter with a Hydrogen-alpha filter?
No, this is not a useful or safe combination. Hydrogen-alpha filters operate at 656.3nm, while this filter operates at 393.3nm. Stacking them would block all light from reaching the sensor. This filter is used in the Antlia Herschel Wedge prism for CaK imaging.
