The Danger of Eyepiece Solar Filters
Channel: tetenterre
Date: 04/08/2011

This is what can happen with eyepiece-fitting solar filters: the focused heat from the Sun can cause them to fracture. The most likely consequence is an injury called photochemical retinopathy, which can lead to permanent blindness.

Don't risk it!

In short, these things should be banned from sale. Instead, they are included with budget telescopes, i.e. those targeted at novice observers, those who are least likely to be aware of the dangers. 

For inexpensive ways of safe solar viewing, see:
http://www.youtube.com/watch?v=eDZ_nDR1BYk

With hindsight I realise that the camera could have been better placed for effect when the filter fractured. I will re-record the demo at the next opportunity.