In this project i have used 60mm achromatic doublet lens with 25 mm metal eyepiece. Scope has a 3 inch by 3 inch secondary mirror. Casing is made of 25 & 12mm rubber wood. Lens is housed in a 70mm Aluminum tube. Here the image of the sun is projected on a white plastic sheet. Scope works on Alt-Azimuth wooden mount, movements are quite smooth as aluminum cradle runs on Teflon pads. There is a small maintenance hatch for focusing the image.
This is a useful scope for schools & colleges for Astronomy presentations. Projection method is safe & effective way to enjoy sun's features.
Peter beat me to it!
In the Ha scope the etalon must be matched with a very narrowband blocking filter...this "blocks out" everything other than the Ha wavelength.
Petr,
The resulting bandwidth of the etalon/ blocking filter combo is only around 0.7 Angstrom (0.07nm).
The blocking filter on its own is about 8-10 Angstrom (0.8-1nm).
So the combo would be far too narrow for effective DSO work, but in THEORY the blocking filter COULD be used for extreme narrow band work.
Also, the small sizes of the available blocking filters (<12mm diameter) would certainly limit the field of view....
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Thats so cool , I like it and thanks for sharing.
