CaK disc comparison between SS and DS

[Merlin66]

Bob,
I would need to measure the individual filter elements to confirm the stacking model accuracy.
I just measured the end result.

[marktownley]

Proms in CaK are pretty easy when the filters are tuned properly, here's my shot from the other night. Sun was about 4 degrees above the horizon at the time and had to use 2x2 binning to get enough light. Filaments are more occasional - easier to see when they obscure bright plage.

CaK-FD-bw by Mark Townley, on Flickr

[MalVeauX]

Thanks Ken,

Interesting so its one main CaK filter and the rest attenuate up to that point?

As for proms & filaments, it's much easier to capture proms in CaK because there's no photosphere behind them, so the surface brightness of the prom vs the void (plus any glow) is similar to how you can lift DSO from the shadow tones with sufficient dynamic range and signal to noise to allow it not just to be seen but also look good and clean. This is incredibly difficult with filaments in CaK because the surface to brightness difference of the filament to the photosphere light is a much smaller delta; same as DSO in heavy light pollution, but even more difficult than that. This is why we need an even more selective filtration system to more easily image filaments in CaK as the filaments/proms are already not nearly as bright as they are in HA, but the disc is still very bright so the surface brightness of the filament is so incredibly low. So we need a very selective CaK filter system with as much photosphere light as possible blocked to increase surface brightness of the filaments/proms in CaK.

Very best,

[MalVeauX]

I look forward to any tests; I unfortunately can't test CaK for this as I only have a Lunt 2.4A B1200 filter for CaK. Always hunting for an affordable second filter to stack with it. But like with HA, it's likely possible to stack filters and push towards selectivity of CaK band and maybe see at least a hint of the filament. I think 1A is insufficient without heavy processing to se notice a filament on the disc (like the big central one today, its not that dark to begin with). The dSHG results tend to be closer to 0.3A where a filament is really seen, and even then, it's more diffuse and less dark than in HA. It's the lower chromosphere and cooler, so maybe this has something to do with it too as there's just less CaK content in a prom/filament and there's more HA content, physically, right? So it would make sense its not going to ever likely be as stark as HA. But it should would be cool to get close to the dSHG results one day.

I'm curious at this point, what CaK filters are even available commercially that are not custom orders?

Very best,

[christian viladrich]

Solar activity is currently pretty low. Even in Ha there is only a very limited number of filaments.
My guess is, even filaments are not seen right now in Ca K, a 1 A filter (or equivalent) will show something when the activity will be back.

[Merlin66]

Bob, et al,
I'm sure I uploaded this spectral profile before....
It shows the DIY stack result and the CWL.
The bandwidth, as measured is 1.0A+/-0.15
As I mentioned, when "un-tilted" (due to focuser sag!) the CWL is sitting just below K3.

Cak filter test 130920.png (60.39 KiB) Viewed 273 times