Thanks everyone for your kind words, I feel humbled.
To answer questions.
I have many scopes (so Mrs Townley tells me), and over time some have definitely migrated into CaK dedicated scopes - the ED80 (stopped to f15) I use for the full disks is very well corrected when stopped down and also high transparency. The 100mm Russian TaL and 127mm Bresser are also excellent, all are used stopped down. IMHO these cheap achromats at CaK perform better than my significantly more expensive LZOS 100/800 - more glass = less light and longer exposure time - not good in CaK.
The CaK module is of my own making, it uses an Alluxa and Chroma CaK filter. Both filters are tilted tuned; the primary filter (closest to the objective) is the Alluxa and this requires only a small amount of tilt to be on band. The secondary filter (closest to the camera) is tilted to be tuned and also throw the reflection away from the disk, as with an external double stack Ha setup. I had experimented with CaK PST filters in the setup, and while these hit the target specification of the filter better than the Alluxa or Chroma, it means they perform better with less tilt, and as such the ghost image is not thrown away from the disk when I use them double stacked. You also get some weird interference patterns. So the benefits of slightly tighter bandpass are negated by ghosting.
Once the ghost disk is thrown away from the 'actual' disk, and coupled with good sky transparency, the proms are easy, they are buried in the last couple of bits of data in the shadows, and require post processing to draw them out, but no different than with a DS Ha setup. Other key is out of band blocking, the more the better. The aim is for as good a signal to noise ratio as possible.
There is more to get out of the system yet - the mechanics of it all are cobbled together out of old extension tubes, filter holders and noses from barlows (minus the lenses). There is baffling and also blacking / flocking of the mechanics which will eek a bit more out. An iterative approach is the way forward.
Despite being imaged at f15 for full disk i'm getting an exposure time of 3ms, and even when I barlow up for closeups I'm keeping below 6ms with minimal gain. I'm very much looking forward to seeing how it compares against the new solar spectrum CaK etalons, I have a feeling I will have a lot more light to play with
Mark
CaK FD 40mm f15 zwo183mm by Mark Townley, on Flickr
CaK FD 40mm f15 zwo183mm colour by Mark Townley, on Flickr
