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Re: [ATM] What filters best for a
> Guy, the filters I used were purchased more than 40 years ago
and
> I suspect the quality was much higher than those available
today.
> I recently looked at the filters available at Home Depot and
they
> were crap by comparison. In truth, it did work and quite well.
I
> used 2 filters together in the light path about 250 mm from the
> eyepiece of an 80mm diameter 1000mm focal length refractor.
The
> views were very good and I never fractured a filter. I did
keep
> the viewing time short though, usually less than a minute and
then
> always moved the scope off the sun. The use of two filters in
> series with the higher ND filter nearer the eyepiece insured
that
> if a filter did break, the light and heat was limited so that
you
> could get away from the eyepiece without damage to the eye.
This
> was before aluminized (or other coatings) solar filters were
> available. I've also been a fan of the Hershel wedge which
when
> used with a good ND filter provides a safe view and still have
one
> that I use regularly, that is when the sun can actually be seen
> from western Washington. I do still use the welders filter in
> front of the objectives of my 9X21 pair of Pentax Mini
binoculars
> just ti get an idea of whats going on. When I was about 7
years
> old, I tried looking at the sun with a magnifying glass and my
> opthomoligist still remarks on the tiny burn on my retina. As
I
> mentioned in a previous email, this posed problems on the rifle
> range when I was in the army but has not caused any other
> problems.
>
> Jarvis Krumbein, in not very sunny Vaughn, Washington
>
> On Fri, 17 Dec 2004 21:00:50 -0800 (PST) Guy Brandenburg
> <gfbrandenburg@yahoo.com> writes:
> > Actually, I tried this (using #14 welder's plate as a
> > filter), and it's a terrible idea - it doesn't work.
> > The reason is that the glass in the filter is not
> > truly flat, and the opposite sides are not parallel. I
> > could find the sun, and it was green, which is OK, BUT
> > it felt and looked like I was lying in the bottom of a
> > very slimy, algae-infested swimming pool and trying to
> > see the sun through about 6 feet of nasty, green
> > water. I read somewhere that this is more of a problem
> > the longer your focal length is. If you have a pair of
> > binoculars, and you can tape two pieces of this stuff
> > over the two objective lenses, it's not too bad. But
> > it absolutely, definietely won't work in a telescope.
> >
> > Get Baader solar filter or 1000 Oaks filter or
> > something similar.
> >
> > Guy
> >
> > --- Ken Hunter <atm_ken_hunter@yahoo.com> wrote:
> >
> > > Art...
> > >
> > > Go to the nearest welding supply shop and tell the
> > > guys what you want to do. Welding filters are
> > > inexpensive and big enough that you can easily try
> > > this yourself to see what you need.
> > >
> > > If you use the filters before the objective, you
> > > need
> > > not worry about the heating of the internals as long
> > > as the throughput is safe to view. If you use the
> > > filters after the objective (near the focus) you DO
> > > have to worry about the heat.
> > >
> > > Ken Hunter
> > >
> > >
> > > --- artbianconi@blast.net wrote:
> > >
> > > > Can anyone tell me the numerical value of a
> > > neutral
> > > > density
> > > > combination that will cut the light of the sun
> > > down
> > > > to something
> > > > safe? Need I be concerned with internal heat
> > > damage
> > > > to the
> > > > mirrors when using filters?
> > > >
> > > > Thanks
> > > >
> > > > Art Bianconi
> > > > Milford, NJ
> > > >
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> > =====
> > Guy Brandenburg
> > Washington, DC
> > My home page:
> > http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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> >
> >
>
>
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