Except during the brief total phase of a total solar eclipse, when the Moon completely blocks the Sun’s bright face, it is not safe to look directly at the Sun without specialized eye protection for solar viewing.
Viewing any part of the bright Sun through a camera lens, binoculars, or a telescope without a special-purpose solar filter secured over the front of the optics will instantly cause severe eye injury.
When watching the partial phases of the solar eclipse directly with your eyes, which happens before and after totality, you must look through safe solar viewing glasses (“eclipse glasses”) or a safe handheld solar viewer at all times. Eclipse glasses are NOT regular sunglasses; regular sunglasses, no matter how dark, are not safe for viewing the Sun. Safe solar viewers are thousands of times darker and ought to comply with the ISO 12312-2 international standard. NASA does not approve any particular brand of solar viewers.
Always inspect your eclipse glasses or handheld viewer before use; if torn, scratched, or otherwise damaged, discard the device. Always supervise children using solar viewers.
If you don’t have eclipse glasses or a handheld solar viewer, you can use an indirect viewing method, which does not involve looking directly at the Sun. One way is to use a pinhole projector, which has a small opening (for example, a hole punched in an index card) and projects an image of the Sun onto a nearby surface. With the Sun at your back, you can then safely view the projected image.
You can make your own eclipse projector using a cardboard box, a white sheet of paper, tape, scissors, and aluminum foil. With the Sun behind you, sunlight will stream through a pinhole punched into aluminum foil taped over a hole in one side of the box. During the partial phases of a solar eclipse, this will project a crescent Sun onto a white sheet of paper taped to the inside of the box. Look into the box through another hole cut into the box to see the projected image.
Those require different types of solar filters. When viewing the partial phases of the eclipse through cameras, binoculars, or telescopes equipped with proper solar filters, you do not need to wear eclipse glasses. (The solar filters do the same job as the eclipse glasses to protect your eyes.)
Seek expert advice from an astronomer before using a solar filter with a camera, telescope, binoculars, or any other optical device. Note that solar filters must be attached to the front of any telescope, binoculars, camera lens, or other optics.
From- NASA
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