Before using a solar filter inspect it thoroughly to ensure it is not damaged. Look for tears, creases, scratches and perforations, no matter how small. In case of doubt, play it safe and don’t use the filter.
Optical instruments with a solar filter (binoculars and telescopes)
The most interesting and dramatic views of the Sun will be through an optical instrument equipped with a standard solar filter. This combination provides the sharpest and most detailed image, however, only one person at a time can see it.
Standard solar filters are made of aluminized Mylar film; or optical glass covered with a thin metallic layer deposited by vaporization in a vacuum. Glass filters are usually mounted in aluminium rings that can be slid over the instrument’s opening. They come in different sizes to suit a range of telescopes and binoculars. Mylar filters are available in similar mounts, and also come in large sheets that can be cut to fit any instrument. Both types are sold at stores that specialize in astronomical equipment.
Solar filters should always be placed over the opening of the instrument to reduce the amount of light entering. In the case of binoculars, both lenses should obviously be covered. Make sure the filters are well secured with tape to avoid accidental removal. (Caution: Some telescopes still come with tiny solar filters that thread into the eyepiece. These filters are extremely dangerous and should never be used: They can crack without warning due to intense solar heat. These filters should be discarded!)