To reduce the half-value width of H-alpha solar telescopes and thus make significantly more details visible on the sun's surface, a second etalon (H-alpha filter) must be used. This combination of two H-alpha filters is called "double stacking".
Previously, it was necessary to equip an existing H-alpha telescope with an additional H-alpha front filter in front of the objective. This method often leads not only to optical disadvantages, such as "ghost images", but is also very expensive, as the front filter must have a large diameter.
The DSII system from Lunt takes a different approach: here, a second etalon is built directly into the telescope. Since this second etalon is not placed in front of the objective, but far back in the beam path, it can be much smaller and therefore also less expensive. The DSII modules have a complete collimation lens system built in, and the optical design ensures a perfect image and prevents ghost images from the outset.
Since the original H-alpha telescope is already equipped with all the necessary energy protection filters and the DSII module is integrated into the telescope, no additional energy protection filters are required. This keeps the image of the sun brighter than is usually the case with other double-stack systems. Even protuberances, which are otherwise greatly attenuated in double stacking, remain much clearer and more detailed.
Finally, the DSII modules are also equipped with the innovative "Pressure Tuner" system, which enables high-precision tuning.
