From David Le Conte, Castel, Guernsey
Karl Erik Birkeland and Fiona Vincent advocate using CDs as solar filters
(Letters, 9 May, p 59).
This is dangerous advice. As Ralph Chou of the School of Optometry,
University of Waterloo, Canada, has pointed out, CDs have a wide range of
optical densities and many are unsuitable for use as solar filters. They are,
therefore, not recommended for this.
London
