The 70mm SolarMax II solar astrograph that I use for solar photography uses two, tunable Etalon filters and multiple broadband filters to create images using only light near the Hydrogen alpha emission line’s wavelength (656.28 nanometers). All of my solar imaging to date has been done with this instrument in what the industry calls double-stack mode; that is, with both Etalons in place.
Here is the scope in single-stack configuration. It looks just a bit stubby with the front-end optics removed.
Today was mostly cloudy, and I decided to see how the instrument would perform with a single Etalon. The single stack configuration still shows the sun in H-alpha albeit with a broader band of light. The result is a much brighter image that is great for showcasing sunspots but not as useful for showing plages, filaments, and prominences. The prominences can be brought out – but only by grossly over-exposing the sun’s disk.
Below is today’s single-stack sunspot image. There are eight named active regions. Of these, AR4094, 95, and 97 are visible if one zooms in on the image, but they are small sunspot groups.
The over-exposed eastern limb prominence is shown below.
This was an interesting experiment, but I am going back to using the double-stack configuration for my routine solar imaging.