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Observing Basics web extra: Tales of screw-in solar filters

The dangers of these accessories cracking from the Sun's heat proved to be more than just a cosmic legend.
January 2010 solar filter
This screw-in solar filter cracked while Dennis O’Connell was turned away from the eyepiece of his secondhand 60-millimeter refractor some 40 years ago.
Dennis O’Connell
Last July, I asked for reader input to help me document the risk of using solar filters that screw into the eyepiece. They commonly accessorized low-budget telescopes made in the 1960s and 1970s — mostly 2.4-inch (60 millimeters) refractors and 4.5-inch (114mm) reflectors, the latter stopped down with 2-inch (50mm) aperture reducers. Here are the e-mail responses I received.

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