make a white light filter
One of the safest ways to view the Sun is to fit a white light filter over the front of your telescope. The resulting view has good contrast and neutral colour. These filters are relatively simple to make using sheets of solar film cut to size. Baader’s AstroSolar Safety Film is available in two grades: OD 3.8 is for imaging only, while OD 5.0 is suitable for visual observing and imaging. OD stands for ‘optical density’, with higher numbers giving you dimmer images. Check your filter for holes and tears each time you’re about to fit it. If you find any, discard the filter and make a new one.
It’s important to also remove or cap your telescope’s finder. This prevents it from being damaged by the Sun’s intense rays and removes the urge to look through it to line up the main instrument. Always make sure the telescope is pointing away from the Sun before fitting the filter. When you’re done observing, do the same – aim the telescope away from the Sun before removing it.
If your telescope aperture is too big to entirely cover with solar film, you can use a mask made from stiff card to cover over it; then cut a smaller hole in this mask and cover that with solar film. Make sure that the mask fits over the entire aperture and that no light can leak around its edges. For telescopes with a central obstruction, such as reflectors or Schmidt-Cassegrains, cut the aperture hole off-centre so the secondary mirror doesn’t block it.