On 2017-08-03, wrote:
This old thread but applies now with 2017 eclipse...

Someone says the numbers DO add up so I figure using two number 10s
from cheap Harbor Freight welding goggles will be okay. I wouldn't plan
on staring at it for extended periods in any case. Would be cool to put
it on front end of telescope and view, but that's pushing it.

With a telescope, the way to go is (assuming that it is on a
tripod) is to mount a white piece of cardboard (or white paper supported
by cardboard) at a proper distance behind the eyepiece, and adjust the
focus so it projects a sharp image onto the cardboard. The more
distant, the larger the image if the focus range is enough.

If the telescope is smaller than the cardboard, put another
piece of cardboard around the back end of the telescope eyepiece, to
make sure that the target cardboard is in the shadow.

If you have a fairly large diameter, mirror lens telescope
(much shorter than the glass refractor only 'scopes for a given power),
you can use a smaller filter mounted off center in some opaque
cardboard, and mount it off center, so it covers the area between the
center mirror mount and the outer rim of the front lens. This reduces
the amount of energy coming through the 'scope, so the filter can be
weaker and smaller than needed for the full aperture of the 'scope.

Long ago
I used 6 polarized filters (crossing two at 90 degrees, then three sets
at 120 degrees) which made it almost black (easy to see sun) but don't
know if it blocks UV and IR. I was stupid (younger..) and used it to
look at the sun through a telescope... didn't take long and image got
blurry (I don't remember seeing the sun) so looked at filter and it was
MELTING...

*Always* put the filter at the input end of the telescope.

dumb bass... remember burning leaves with sun using mag glass
and a telescope is much more powerful... glad I didn't burn my eyeballs
(am 60 now so damage from 40 years ago would be apparent).

Yes.

Good Luck,
DoN.

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