There is
oodles of detail in the closeup shot of relatively dormant active region 12042
seen in this shot taken with the homebrew CaK filter and the 80mm scope running
at 2000mm focal length. I would love to have perfect seeing and be able
to double or even treble the focal length as i'm certain the closer in you look
at CaK the more detail that is recorded. I'm really pleased with the work
i've been able to do on my CaK filter over the easter fortnight; after much
changing of the order and spacings of the filter elements I now have a setup
where the reflection / ghost images are not consequential or significance in
the final image. I have also learned that in it's native state the PST
CaK 'magic' filter is actually tuned slightly higher than 393.37nm so that when
it is used in an f10 light cone the centre bandpass is blue shifted to exactly
CaK (393.37nm) wavelengths. I knew that in a light cone of less than f10 that
the resultant image was washed out in a way the same as I got when tilting the
filter elements to try and throw the reflections, and that by tilting the
filter results in a blue shift of the bandpass wavelength. However I was
really surprised when I ran the filter setup in a 50mm f20 native light cone
and the resultant image I got was also washed out and lacking in both contrast
and detail. This led me to the conclusion this was a result of the
filters bandpass wavelength being red shifted as it was operating in a
shallower light cone than it was designed for. What is for certain is
that I will be using the filter setup in a f10 light cone whereever possible as
this gives the most contrasty and detailed results by far. The 80mm
running at a native f12.5 before any barlowing is used seems to escape any
significant or noticeable red shifting as the closeup images from the past
couple of days show. All my full disks though I will be taken using the
40mm at f10, with 2x barlow, as I have also seen that the 0.5x reducer at the
short wavelengths of CaK introduced contrast robbing spherical aberration.
All of the disks I have taken so far have shown to be far better with the
40mm f10 and 2x barlow than the 80mm f12.5 and 0.5x reducer; it would be
interesting to see the result of using the 80mm at f12.5 to get a full disk,
but this would need the best part of 16 frames, and the chances of the seeing
holding out for all of them is probably only something that would happen a
couple of times a year. For every large aperture CaK image like above and
those below, there are probably 10 discarded for each good result. Maybe
it is time for a camera with a larger chip? Hmmmm...