On Thu, 17 May 2012 15:22:39 -0500, Snag wrote:

mike wrote:
I want to look at the eclipse this weekend. Everybody says a #14
welding shade is good. I don't have one.

So, how do the numbers stack up when you use 2? I'm guessing it's not
linear, so 7+7 doesn't = 14???

What's the math for stacking welding shades?

Thanks, mike


A much better idea is to punch a pinhole in the center of one end of a
shoebox , and tape a piece of white paper inside the other end . Point
the pinhole end at the sun , there will be an inverted IIRC image of
the sun on the paper if you've lined it up properly . Similar in
principle to a pinhole camers , you might google "pinhole eclipse
viewer" or similar for more info .
Welding lenses are not really suitable for viewing the sun , though
many
people do it ...;

If you have a room available that's sunny at the time of day of the
eclipse, cover up the windows and make a pinhole in the shade. You get a
lot bigger solar disk to view, and if you want you can make multiple
holes.

Because you need to make a tradeoff between brightness and focus, you
want a bigger "pinhole": if I recall correctly a 1/16" or even 1/8" is
appropriate for a ten foot distance.

I remember one solar eclipse where, after leaving the building where us
engineering staff had converted a conference room into a solar
observatory, I noticed that the little sun-dapples filtering through the
leaves of the trees were all little solar eclipse pictures.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com