If you already have an achromatic or apochromatic refractor telescope, you don't have to buy a complete Calcium-K telescope as this module can be directly used in your refractor telescope up to 100mm aperture and 540mm focal length. This will convert it into a complete Calcium-K solar telescope. You'd need a telescope that accepts 2" accessories as that's the size of the modul.
Just replace your 2" eyepiece with this modul and you are ready to go.
The internal narrowband filter in this module allows for a <2.4 Angstrom bandwidth.
Please note that the Ca-K wavelength is at the edge of the visible light spectrum for human eyes, so for most of us visual observing in this spectrum will be difficult. However, all details could be captured photographically. Therefore the Ca-K Module is optimized primarily for imaging.
For telescopes up to 100mm aperture and up to 540mm focal length. For imaging it will be better to use a bigger Ca-K module (i.e. the bigger the blocking filter the better...).
The Ca-K module is in a 90° star diagonal, for 2" focuser on the telescope side and with T2 connection and for 1.25" eyepieces on the eyepiece side. If you want to try to do some visual observations by using your 2" eyepieces, there is a 2" eyepiece holder adapter available separately.

• Lunt Ca-K module with  internal etalon
• B600 Blocking Filter in star-diagonal for enhanced viewing and photography