Had a customer ask me why he couldn't find one those solar filters that attach to an eyepiece of a telescope, like the one supplied with the telescope he had when he was a kid. I told him to count his blessings. It would be better if he did not find one.

A solar filter that attaches to an eyepiece is simply dangerous. Should the filter crack, the full brunt of solar light as well as the heat being "collected" by the telescope immediately enters the eye, instantly resulting in a burned retina and that awesome amount of heat also makes it likely that the filter will fail. Think back to the days when you played with a magnifier and tried to start a fire. A telescope concentrates many hundreds of times as much heat.

A solar filter belongs on the front of the scope. Should it crack, only a very small amount of light enters the eyepiece and, furthermore, most of the heat from solar radiation is stopped before it ever enters the system. Better yet, buy a solar telescope designed specifically for observing the sun, such as the Coronado PST.

Please, anyone who finds a solar filter that attaches to an eyepiece at a garage sale or flea market, throw it away. You may be preventing someone a real tragedy.