Greg, you've done your research. Well done. I recall a similar report stating that #12 & up were "safe". Welder's glass filters are great for inexpensive, non-magnified views of the sun, but the contrast is so poor that they should be considered only if no other proper filters are available. C. --- Greg Taylor <astronomus_maximus@yahoo.com> wrote:
Elsewher one their site I found:
Filter Transmittance
The luminous transmittance of the filter, when determined as described in clause 6 of EN167, shall not exceed 0.0032%. Filter transmittance in the waveband 280 to 380 nm (ultraviolet radiation) shall not exceed 0.003% at any wavelength. Transmittance in the near infrared waveband (780 to 1400 nm) shall not exceed 0.027% at any wavelength. Filters with luminous transmittance (in the waveband 380 to 780 nm) equivalent to scale number 12 to 16 as specified in Table 1 of EN169:1992 are considered suitable for direct observation of the sun. It should be noted that many observers will find the solar image uncomfortably bright when filters with scale numbers of 12 or 13 are used.
--- Patrick Wiggins <paw@trilobyte.net> wrote:
Greg Taylor wrote:
I just picked up some #13 Welder's glass. The
spot is
very easily seen naked eye. I need to get a solar filter for one of my scopes.
I don't know that a #13 is safe. #14 is the only one I've heard is safe.
http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/eclipsePhoto.html#Safety
Patrick
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