Dangers with solar projection?

Hi all.

I just got a recipe on how to use a spotting scope for solar projection.
The scheme involves reducing the scope aperture to some 30 mm and using
a plate as shield to provide some shadow for the projection screen.
A nice picture is provided that shows an example of a projection setup.

So far so good.

Now, the text states that "only eyepieces that do *not* contain glued
lens elements should be used for solar projection".

So, I'm wondering:

- What are the dangers to the equipment involved when doing solar
projection? I am very well aware of the dangers to the eyes when
observing the sun without proper filters.

- How do I find out whether my eyepiece contains glued lens elements
or not?

- Could one barrel of a roof prism binocular be used for solar projection?

Thanks in advance for any help,

Rune

Thanks in advance for any help,

Hi Rune:

My advice? Don't do it. Even if your eyepieces do not contain glued
elements--and most modern designs probably don't, you can still cause severe
damage in the scope itself due to heat buildup in the OTA. Especially, do not
do this with MCTs or SCTs. Many modern binoculars use plastic components
internally that can be damaged by heat, too. And there's always the danger of
somebody putting her/his eye up to the eyepiece. Get a good full-aperture solar
filter if you want to view the Sun.


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

I emphatically second Rod on this!

A safe, modestly priced filter can be made from Badder solar film using
directions as found in the "Technical Support" section of the Astro-Physics
site:

http://www.astro-physics.com/

Besides... the views will be light years ahead of some dark shadows cast on
a pie plate:

http://www.astro-nut.com/sun.html

Give your eyeballs a treat... they deserve it!

Cheers,

Paul

--- http://www.astro-nut.com/ ---



from
"Rod Mollise" wrote in message
...

Thanks in advance for any help,

Hi Rune:

My advice? Don't do it. Even if your eyepieces do not contain glued
elements--and most modern designs probably don't, you can still cause
severe
damage in the scope itself due to heat buildup in the OTA. Especially, do
not
do this with MCTs or SCTs. Many modern binoculars use plastic components
internally that can be damaged by heat, too. And there's always the danger
of
somebody putting her/his eye up to the eyepiece. Get a good full-aperture
solar
filter if you want to view the Sun.


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Hi Rune,
I have had great results using a 60mm, 700mm fl Celestron Guide scope
and some old .965 eyepieces. I've used this setup on several occasions
when doing solar observation for an entire elementary school over a
period of six hours without damage to either the telescope or an
eyepiece. In neither instance did the telescope heat up excessively. I
would point out that you do have to be careful to insure that no one
tries to use the projection end for visual viewing! I projected the
image onto a lightly colored (have used florescent yellow and orange)
foam mat board with great results. Using a white board tended to be
rather bright ... This year I did the same and used a Meade 26 mm .965
Plosel with excellent results.

Clear skies

Harry

Rune Allnor wrote:
Hi all.

I just got a recipe on how to use a spotting scope for solar projection.
The scheme involves reducing the scope aperture to some 30 mm and using
a plate as shield to provide some shadow for the projection screen.
A nice picture is provided that shows an example of a projection setup.

So far so good.

Now, the text states that "only eyepieces that do *not* contain glued
lens elements should be used for solar projection".

So, I'm wondering:

- What are the dangers to the equipment involved when doing solar
projection? I am very well aware of the dangers to the eyes when
observing the sun without proper filters.

- How do I find out whether my eyepiece contains glued lens elements
or not?

- Could one barrel of a roof prism binocular be used for solar projection?

Thanks in advance for any help,

Rune

(Rod Mollise) wrote in message ...

Thanks in advance for any help,

Hi Rune:

My advice? Don't do it. Even if your eyepieces do not contain glued
elements--and most modern designs probably don't, you can still cause severe
damage in the scope itself due to heat buildup in the OTA. Especially, do not
do this with MCTs or SCTs. Many modern binoculars use plastic components
internally that can be damaged by heat, too. And there's always the danger of
somebody putting her/his eye up to the eyepiece. Get a good full-aperture solar
filter if you want to view the Sun.

Thank you for the warning. I'll try to get the filters.

Rune

Throughout high school, I did several public demos with a solar telescope to
highlight various events such as partial eclipses, transits, etc. The
school had a cheap 3" newtonian, in which the only glued part was the
secondary mirror, so which I reglued the mirror using high-temp epoxy.

For eyepieces, just make sure they are eyepieces you wouldn't mind
accidentally destroying. I usually find cheap binoculars at garage sales
and pawn shops, take out the set screw, and remove the eyepieces. Now I
have two decent eyepieces for around $15 or $20. I just wrap the eyepieces
in heavy paper to make them fit in my focuser. They aren't suited for deep
sky work, but I have yet to have one go bad.

The real danger of doing solar projection is that during the brief second
that your back is turned, someone will look in the eyepiece and sear their
retna. To prevent this, I made sure that there was no access whatsoever to
the eyepiece. I ordered a 1.5' by 1.5' piece of rear-projection TV screen
(I forget the exact source, but it was an educational supplies catalogue),
and mounted it on the open end of a largish cardboard box. I cut a hole in
the other end of the box for the eyepiece to fit through, and a side hole to
give me access to the focus knob. Then, I just placed the box over the
eyepiece (and secured it with some nylon straps), and I had a safe solar
telescope for public viewing.

-- Zan Hecht

In article ink.net,
Zan Hecht wrote:


The real danger of doing solar projection is that during the brief
second that your back is turned, someone will look in the eyepiece
and sear their retna.

When I have shown shoolkids sunspots by the projection method, they
have sometimes asked if they could look directly into the eyepiece.
Instead of giving them a lecture why they shouldn't do so, I asked
one of them to put their finger right behind the eyepiece instead.
Within a second, the pain in the finger made that kid realize why it
would be a very bad idea to put his eye there.... no other kid
wanted to try to put their finger there - they understood....

Regarding eyepiece projection, that is best done with a small
refractor, for two reasons: first, the aperture is small which limits
the amount of heat entering the telescope, and second, there's no
secondary mirror to worry about. But the eyepiece should be reserved
for solar projection - you shouldn't use any of your other eyepieces
doing this.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

(Rune Allnor) wrote in message . com...
Hi all.

I just got a recipe on how to use a spotting scope for solar projection.
The scheme involves reducing the scope aperture to some 30 mm and using
a plate as shield to provide some shadow for the projection screen.
A nice picture is provided that shows an example of a projection setup.

So far so good.

Now, the text states that "only eyepieces that do *not* contain glued
lens elements should be used for solar projection".

So, I'm wondering:

- What are the dangers to the equipment involved when doing solar
projection? I am very well aware of the dangers to the eyes when
observing the sun without proper filters.

- How do I find out whether my eyepiece contains glued lens elements
or not?

- Could one barrel of a roof prism binocular be used for solar projection?

Thanks in advance for any help,

Rune

Hi
Use a f/375 3.68" primary and a flat. The light is
never more concentrated than direct sun light and produces
a 1 foot sun on a screen. Anyway, it works for me.
I wish I knew a good source for such lenses but I don't.
I found mine at a swap meet.
Dwight