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There are a couple of other options for solar viewing.
My favourite is a long focus mirror fed by a driven flat mirror. My version had a 4 inch mirror of 47 feet focal length which gave a solar image 5 inches across…i.e. bigger than the mirror! So although the sun if focussed the surface brightness is less than that of direct sunlight. Sorry I don’t have any images but there was a short piece in Astronomy Now, November 2008 page 75. Not an original idea by me…Hale made a 100 foot solar telescope which was described in detail in volume 1 of the Amateur Telescope Making books.
The other option is to have a heliostat feeding light through a single lens (no need to be achromatic) with the image viewed through an H alpha filter as usual. A nice example is shown in Sky & Telescope, August 1980, page 162. The 24 foot focal length lens gives very detailed views of prominences etc.
These set-ups are obviously much more involved than conventional methods but would make nice projects for astronomy clubs. They have the advantage of having all the optical elements on show so people can see how they work.
Mike.Richard,
Worth giving the Astronomer’s Telegram reference for the image above for additional information: Astronomer’s Telegram #17264Interesting trajectory for this object, almost in the plane of the ecliptic. Odd for an interstellar object given the solar system is tilted about 60 degrees from the galactic equator. How does it compare to the other two known interstellar objects?
Mike
