I always was sort of fascinated by the idea of an electronic filter of the Quark,
So I'd like to know more about double stacking, can you give me some idea of what that is?
Double stacking is two etalons (HA comb filters) and a single blocking filter working together to get rid of any parasitic continuum light from the photosphere. The photosphere is incredibly bright, much brighter than the chromosphere, so when you try to view HA, you have to block out the photosphere to do that, and it requires very, very narrow filtration to get there. The photosphere is underneath the chromosphere, and its brighter, so if you think about how challenging it is to block the light of something under the structures you're trying to see, that are dimmer, you're presented with a challenge. So if we can block the photosphere's light and only see a single wavelength of light, we can start to see just that, and see the chromosphere's fiery hell scapes. With a single stack, some parasitic continuum bleeds through, so you will see less contrast on the disc surface due to the brighter photosphere coming through, but the limb will be unaffected so prominences will be bright and fine, but you will see a double limb effect, as you see both the layer of the chromosphere (dimmer) over the brighter lower photosphere, at the same time (which is a super interesting concept if you think about it). There's less contrast on the disc with a single stack because of the brighter photosphere bleeding through. Double stacking without another HA etalon is a means to then further filter things down, basically it trims the wing profiles of the transmission curve so that the off-band light is blocked even more, and the peak of transmission in HA then is sharper, narrower (ie, greater finesse). The bandpass number is irreverent to the results (ie, the sub-angstrom value, like 0.7A or 0.5A, etc). So blocking the off-band wavelengths of light that form the wings of the transmission profile, it will block that last bit of unwanted photosphere light and so then the disc is higher contrast because it no longer has photosphere light bleeding through, and when tuned together, no longer has a double limb, the effect is a disc that is the same brightness at the limb with the proms as it is on the disc itself with its features and way higher contrast on the disc features (filaments, plages, etc) and much easier to see individual spicules, mottling, etc. This cannot be done with a single etalon filter (even a $16,000 0.3A Daystar Quantum will show a double limb!).
Once you view through a double stack, you will hardly be able to view a single stack again. Just a preference though. There are those that prefer a brighter single stack view. Single stacks are great for the limb structures like prominences. But if you like the disc structures too, a double stack just makes such a profound difference. A double stack is dimmer, the sharp peak transmission is lowered as each etalon grinds away 45% of the transmission each time. So viewing is just like viewing night time (dark adapt, wear a shroud, block ambient light, etc) and so some just prefer a brighter view, but again, the contrast difference is huge.
For me, I have 150mm and 200mm solar scopes. I used my Quark in them for high res, large aperture single stack views. But, my preference for visual HA strongly favors the high contrast of a double stack. I vastly prefer my small 60mm double stack for visual HA over my much larger single stacks.
150mm & 200mm single stacks with Quark & Binos:
120mm Quark & Binos:
40mm (ST80) Quark & Binos:
60mm double stack with Binos (my preference for fast visual):
Edited by MalVeauX, 12 August 2020 - 11:40 AM.