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From: lutz@ur-tut.UUCP (Dave Lutz)
Newsgroups: sci.astro
Subject: Solar filters
Message-ID: <779@ur-tut.UUCP>
Date: Wed, 15-Oct-86 17:35:12 EDT
Article-I.D.: ur-tut.779
Posted: Wed Oct 15 17:35:12 1986
Date-Received: Wed, 15-Oct-86 21:57:36 EDT
Organization: Univ. of Rochester Computing Center
Lines: 39
Keywords: :-(


    A few weeks ago I submitted a question about the safety and
usefulness of welders glass as a telescopic solar filter.  I would
like to thank the many people who responded.  The following is a
summary of the responses I got.

    Most people advised against looking at the sun directly with a
telescope at all no matter what type of filter you are using.  The
chance that your filter might be damaged allowing the direct sunlight
to hit your unprotected eye is just too great.  This is especially
true when using an in-the-eyepiece filter because the heat generated
by the concentration of sunlight can crack the filter.  The only
truly safe way to view the sun is the projection method.

    Concerning the usefulness of welders glass as a filter most
people advised against it.  Welders glass is not intended for this
use and it is not optically flat.  This means that the image could
have severe distortions in it.  It is especially poor for first
hand viewing because it does not block the full spectrum of infrared
and ultraviolet light.  This means that even though you may not feel
it you have a very good chance of damaging your eyes.  One person
stated that he had looked at the sun very briefly through welders
glass and has experienced some loss of vision.  He stated that it
is not noticeable during the day but he has problems looking at
faint objects through his telescope.:-(

   A few people said that there was an article in Sky and Telescope
 concerning the issue of solar filters and viewing the sun.  It is
supposed to be a very good article and it even deals with the question
of using welders glass for this purpose.  I'm sorry to say that none
of them could remember what issue it was in.  If you can find it it
would be a good article to read if you're interested in the sun.


Thanks again for the many responses.


Dave Lutz
allegra!rochester!ur-tut!lutz