How does a solar filter work?
October 13, 2008
Solar filters are absolutely essential for observing the sun safely with your telescope. Our star is so bright it can permanently damage both your eyes and the scope’s optics unless both are properly protected.
Full-aperture solar filters are by far the safest filters and also give the benefit of the full resolution (ability to see fine detail) of the telescope. They fit over and cover completely the front-end of the telescope. Sub-aperture solar filters that fit on a smaller opening on an opaque tube or lens cap are also safe, but reduce the resolving power of the scope to that of a lens or mirror the diameter of the small opening.
Solar filters work by reflecting away most of the light and heat before it gets into the tube. Only 1/100,000th or a millionth of the light actually passes through. Aluminized Mylar is the most common material, though metal-on-glass filters are also popular.