Why Magnesium I (b2)-line?
Magnesium is a highly magnetised chemical on the sun. The temperatures for energetic activity emitting this line are calculated to be extremely high. Spectroscopically, a line "splitting" called the Zeeman effect can be observed, whereas the dark absorption "splits" and occurs slightly above and below the typical wavelength where light from non-magnetized activity is absorbed. Strong absorption can be seen spectroscopically at 5172Å.
TViews in Magnesium reveal plage, large scale magnetic structure and dark absorptive mottling of the chromospheric structure. The line is brighter than Calcium, Hydrogen Alpha and even Sodium. So it's going to be very easy for observers to see and the exposures will be very short.
For use on F4 - F/8 focal ratio refractors