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Can emergency blanket material be used for making a homemade solar filter for use with a digital camera? It seems to be aluminized Mylar.

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    $\begingroup$ There are a lot of different brands of these, so it would be impossible to give a generalized answer other than "No". These aren't designed for such use, and it's highly unlikely they'd achieve the correct levels of blocking by accident. $\endgroup$ Commented Apr 5 at 15:45
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    $\begingroup$ Perhaps we need a canonical post to answer "Can I use X to make a homemade solar filter?" $\endgroup$
    – James K
    Commented Apr 5 at 17:12
  • $\begingroup$ There is an international standard; see my answer below. $\endgroup$
    – Geremia
    Commented Apr 6 at 4:25

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NO!

Do not do that. It will damage your eyes.

They do not offer protection for all wavelength, and might not offer enough attenuation so that too much or invisible radiation penetrates it and WILL damage your eyes. See also https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/safety/ and this article from scientific american.

Solar filter foil does not cost a leg. Get that or directly dedicated eclipse glasses from a trusted manufacturer.

If you are unable to obtain any decent solar eclipse gear, use make-shift gear to project the image of the sun (like shown on both pages I linked). That's easy and allows several people to see the same image concurrently and enjoy jointly.

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  • $\begingroup$ What if you use multiple layers? $\endgroup$
    – Geremia
    Commented Apr 4 at 21:17
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    $\begingroup$ Still don't. Absolutely don't. You have two eyes. Are they not worth more than 1$ or 1€? A cane certainly costs more. You do not know the complete transmission spectra for these materials from x-ray to FIR. Thus if it is transparent to UV or certain infrared wavelength - multiple layers won't help, and you will still get a sunburn or worse on your retina and call for a damaged eye lens. The invisible radiation is at least as dangerous as what you actually see. Don't use welding glasses either for the same reasons. $\endgroup$ Commented Apr 4 at 21:22
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    $\begingroup$ @planetmaker, a #14 welder's glass (the darkest standard shade) is sufficient protection for watching a solar eclipse. Prior to the advent of metal-film solar glasses, it was the preferred form of protection. $\endgroup$
    – Mark
    Commented Apr 4 at 22:03
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    $\begingroup$ @Geremia If you measure the attenuation and determine that it meets standards over the full spectrum, anything is fine. Do you have the equipment and expertise to do that? $\endgroup$
    – John Doty
    Commented Apr 4 at 22:21
  • $\begingroup$ You are right @Mark.i Was indeed thinking of smoked glass $\endgroup$ Commented Apr 5 at 5:54
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The aluminized Mylar of a space blanket is not subject to the same quality controls as solar filters. In particular, it may have pinholes that create pinhole burns on your retina, and it may have variable coating thickness producing a patchwork of safe and unsafe areas. In addition, the average person is only able to judge the optical quality of the blanket in visible light; most eye damage is done by infrared and ultraviolet light.

Solar filter for a cheap webcam? Sure. Solar filter for your eyes? No.

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"Eclipse Filters: Time for an International Standard" by B. Ralph Chou, MSc, OD Associate Professor; School of Optometry, University of Waterloo;Waterloo, Ontario, Canada, N2L 3G1 and Registrar College of Optometrists of Ontario:

Filters for visual and photographic use

Acceptable filters for unaided visual observations include: aluminized polyester specifically designed for solar viewing, shade 12 and 14 welding filters, black polymer filters (Thousand Oaks Solar Shield 2000 and Rainbow Symphony Polymer), and two layers of fully exposed and developed silver-bearing black and white film negative. For photographic and visual use, particularly with binoculars or telescopes, acceptable filters include: aluminized polyester specifically designed for the purpose, and Questar and Thousand Oaks T1 and T2 glass filters. The Thousand Oaks T3 filter should be used with extreme care for photographic use only.

Not recommended are: metal-coated polyester that is not specifically intended for solar observation, smoked glass, floppy disk media, black colour transparency (slide) film, floppy disk media, and compact disks (because of the inconsistent quality of the metal coating).

source 🎩-tip Mike G

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There is an international standard:

ISO 12312-2:2015(en) Eye and face protection — Sunglasses and related eyewear — Part 2: Filters for direct observation of the sun (cf. unpaywalled version from AAS):

ISO 12312-2

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    $\begingroup$ You can edit your previous answer. $\endgroup$ Commented Apr 6 at 5:23
  • $\begingroup$ Please use edit to combine your two answers $\endgroup$
    – Rory Alsop
    Commented Apr 8 at 9:38

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