Solar Filters

Although eyepiece projection is a convenient and safe method for Solar Viewing, particularly for groups of people, it has its own problems of screen contrast (for outdoor setups) and loss of definition. There is also the ever present risk of damage to the eyepiece, particularly if the image moves off centre. There are numerous Solar Filters available which allow direct viewing, and of course also facilitate photography. Some are quite expensive, but I have found Baader Solar Film to be perfectly adequate and extremely economical. A couple of sheets, costing about £25 (available in the UK from SCS Astro) provided sufficient film for me to make filters for both my telescopes and finders, with some left over. This film received a very favourable review in the September 2000 issue of Sky and Telescope.

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The standard method of construction is to make two cardboard rings to fit the front of the telescope, one sliding on top of the other, and then trap the edge of the film between the rings. I also smeared adhesive on the inner and outer mating surfaces to ensure a safe assembly. This was fine for the 80 mm 'scope and the two finders, but the C8 aperture was too wide for the A4 sheet, so I had to reduce the diameter of the film mount. Possibly a slight loss of contrast and resolution due to the increased ratio of central obstruction to aperture, but not a problem in practice - atmospheric distortions on a sunny day are far more noticeable.

The image is a nice pearly white colour - very natural looking. Before using the filters I always check them for faults, but the film is surprisingly strong and easily withstands normal handling.

Coming shortly - a filter for a Red Dot Finder.