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Solar Observation - a contribution by Derek Hatch
The coronagraph works by placing a small metal cone in the light path of the main instrument at the "prime focus" position to eclipse the image of the Sun . The combined images of Sun and cone are then projected down through a series of lenses and diaphragms to the eyepiece. It is rather like having two telescopes stuck together. To focus you have to focus the view of the cone through the coronagraph and then focus the main telescope for the Sun. A coronagraph does not actually show the corona but allows you to view any prominences and flares erupting from the surface of the Sun.
The pictures above are examples of what can be seen through the coronagraph. The prominences at left is almost 100,000 kms high, 8 times larger than the diameter of the Earth.!
As a comparison to the coronagraph, below are two views from the recent total solar eclipse on February 26th, from Antigua in the West Indies. They were taken using my TeleVue Pronto plus x2 Barlow (f22) and show prominences, the solar chromosphere and a small amount of the inner corona.
If you are interested in coronagraphs, Thomas
Baader can be contacted at:  
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On
the left is a view of the rear end of my 6" Astrophysics refractor fitted
with the coronagraph plus a TeleVue Pronto 70mm refractor and Daystar filter
piggy backed. The coronagraph is made by Thomas Baader of Munich and
includes a 10 Angstrom Hydrogen Alpha (Ha) filter. The Daystar is a
0.6 Angstrom Ha filter, used to view surface features on the Sun.
This is the
same prominence with two x2 converter lenses in front of the camera. As the
focus of the system is fixed it is not possible to use a Barlow lens or eyepiece
projection to enlarge the image.
