The mylar composite used in floppy disks seems opaque... to visible light. 54% of the Sun's energy output is in other wavelengths. There is no certification that a floppy disk cookie will block those. Plus it has a big hole in the middle, danger of inadvertent viewing.
This is like the argument I have with other photographers every eclipse when they try to use their 'super-dark' neutral-density filters. Sure they block ten stops of light, but the IR and UV just sails on through.
Unless it's designed and certifed as a Solar viewing material just don't even contemplate it. You're better watching the eclipse on TV in that case.
> Unless it's designed and certifed as a Solar viewing material just don't even contemplate it.
People have been using dark pieces of photographic film to see eclipses since ever. I wonder if there has been studies on its UV transmissibility
Thought you're right about the super-dark film and I don't think those are dark enough even on the visible range
Though I do agree if you want to stare at it directly your best choice is to get solar viewing glasses (preferably not a fake one)
This page has some tests: astronexus.com/gatfaq/solar-filters besides poor optical quality floppy disks allow wavelenghts > 800nm to pass (this is IR range)
A good suggestion that seems easy to obtain: welder's glass
> People have been using dark pieces of photographic film to see eclipses since ever.
Fully exposed and developed black and white film is safe, color negative film, however, is totally unsafe, regardless of how dark it might seem. The film has to contain real silver particles, not color dyes.
Beware of monochromatic film that looks black and white but it’s really a color negative film developed using C41 process. It has to be real black and white film.
I may be "old school" but the "traditional" way is to use a welding mask glass, something you can usually buy "around the corner" for a very little amount of money and I see that NASA also advises about it:
>One of the most widely available filters for safe solar viewing is a number 14 welder's glass, available through welding supply outlets.
And both colour fim and non-silver B&W film are listed by them among the unsafe:
>Unsafe filters include color film, some non-silver black and white film, medical x-ray films with images on them, smoked glass, photographic neutral density filters and polarizing filters.
Another longer article on that same site (by a different author) actually mentions the grandparent's suggested method of looking through a floppy disk medium:
> Many experienced solar observers use one or two layers of black-and-white film that has been fully exposed to light and developed to maximum density. The metallic silver contained in the film emulsion is the protective filter. Some of the newer black and white films use dyes instead of silver and these are unsafe. Black-and-white negatives with images on it (e.g., medical x-rays) are also not suitable. More recently, solar observers have used floppy disks and compact disks (both CDs and CD-ROMs) as protective filters by covering the central openings and looking through the disk media. However, the optical quality of the solar image formed by a floppy disk or CD is relatively poor compared to mylar or welder's glass. Some CDs are made with very thin aluminum coatings which are not safe - if you can see through the CD in normal room lighting, don't use it!! No filter should be used with an optical device (e.g. binoculars, telescope, camera) unless it has been specifically designed for that purpose and is mounted at the front end (i.e., end towards the Sun). Some sources of solar filters are listed in the following section.
> Unsafe filters include all color film, black-and-white film that contains no silver, photographic negatives with images on them (x-rays and snapshots), smoked glass, sunglasses (single or multiple pairs), photographic neutral density filters and polarizing filters.
This second NASA author seems to believe that floppy disk media (with the hole covered) may actually be safe for eclipse viewing, just not very effective.
It seems opaque, but it is transparent enough to see the sun