The suppliers of some cheap refractors supply a welder's glass filter (pictured left) that screws on to the eyepiece. DO NOT USE THESE! They may heat up and crack as you are looking through the telescope.A proper solar filter always goes on the front end of the telescope, blocking the sunlight before it enters the optical system. Thanks to the Orion Telescope Center for the loan of this unsafe filter. Orion does not sell these! They just had one around as a bad example... They are good and knowledgable people.