Observing the Sun with an optical instrument is extremely dangerous. The concentrated energy from the Sun damages the human eye or a camera. Therefore, there is a wide range of filters available that reduce the light from the Sun. Generally, any telescope with a closed tube (i.e. not a truss-tube) can be converted into a solar telescope.
Filters can be distinguished between those that are mounted in front of the telescope lens and those that are attached to the front of the eyepiece. The former is especially safe, because dangerous radiation does not enter the telescope at all.
Another distinction is whether the filter simply reduces the light, or whether it allow only certain spectral lines to pass through. The first variant is also called a white light filter. These filters preserve the natural view of the Sun and enable the photosphere with its sunspots to be observed. The second variant is usually seen in H-Alpha filters. These allow only a certain wavelength of hydrogen atoms to pass through, and show the structures of the Sun's chromosphere.