http://www.alpo-astronomy.org/solarblog/?page_id=200"The most simple method of observation in searching for
WLFs, is to just use a mylar-type filter. The blue image of these
filters, normally detested by amateurs, is quite close to our
target wavelength. This is also the safest way to look for these
flares. These filters are also very good and showing faculae
associated with these complex groups, well in towards the center
of the disk. Only the highest quality filter should be used.
There are some filters on the market and some homemade out of
lesser quality materials. These show a good deal of sky
brightness just off the limb of the Sun. Such filters will
probably scatter enough light to obliterate all but the brightest
flares.
The author has seen several using the so-called “neutral
density” filters but it would have been impossible without the
prior experience with more selective filtration. "