Solar projection, is it safe?

orestis · #1 16-10-2010, 04:00 PM

Hi guys,

I found an old 50mm department store refractor and thought of trying solar projection out and well i tried without an eyepiece and moving the paper focused the sun image but having an eyepiece in i could not focus it.

Anyway the image was small but very bright just wondering if this is safe

.I even put sunnys on and it was still very very bright and my eyes hurt afterwards as it left a small after image.

I heard this is a safe way of observing the sun.Is it?

I tried to find sunspots but didn't have any luck.

Thanks in advance
Orestis

michaellxv (Michael) · #2 16-10-2010, 04:22 PM

It's safe for you but it may not be safe for your scope. Make sure you have removed the finder, and don't leave it unattended.

Without a solar filter in front of the objective you are exposing the scope to the full heat of the sun. You average dept store refractor will have plastic parts that will probably melt.

Alchemy (Clive) · #3 16-10-2010, 04:30 PM

I took the day off for the last transit of Venus and had it on the ceiling in the front room, it worked, but I would not be using a good scope or eyepieces, I just used an old 90 mm achromatic I have lying around that if it got damaged I wouldn't care, definitely don't leave it unattended.

that_guy (Tony) · #4 16-10-2010, 04:56 PM

get yourself a generic solar film... they work a treat and its a whole lot safer than projection.... and you can also image

asimov (John) · #5 16-10-2010, 05:01 PM

As noted: Safe for you, not necessarily for the scope. I used to do it all the time when I was a kid with a 60mm spotter. No such thing as plastic on scopes back in those days though ;-)

orestis · #6 16-10-2010, 06:13 PM

thanks guys,

Yeah the telescope i was using does have plastic bits so i'm never going to use that again.

I think i might buy myself a white light filter but there is hardly any sunspots these days anyway.

regards orestis

Merlin66 (Ken) · #7 16-10-2010, 07:48 PM

Definately the Baader Solar Film is the way to go!
110% safe (when applied properly) and it will allow you to see the surface detail better.
Don't worry, the new solar cycle is just beginning... in the next few months you'll start to see more and more activity. Now is the time to practise.

Rob_K · #8 16-10-2010, 08:15 PM

Hi Orestis - yeah, agree about the solar film. I have a little bit kicking around, should be enough for a filter for your scope. They're easy to make, out of light card. You're welcome to it - just pm me if you want it.

Cheers -

Rob_K · #9 16-10-2010, 08:17 PM

Oops, should add that it's Baader AstroSolar Safety Film, safe for visual observation of the Sun.

Cheers -

Max Vondel (Peter) · #10 17-10-2010, 12:48 AM

Sure projection is safe.
I remember using my 8" newtonian
with a basic 25mm kellner(remember that name!) eyepiece.
projecting an image 14-16" across.
The granulations stood out, the little lines around the sunspots blazed.
In fact some of my best views of the sun!

Compared to the full solar screens, projection is much better in my opinion. So in desperation I'm now heading towards a Lunt Hershel wedge with 90mm WO refractor and H alpha mounted besides.

mental4astro (Alexander) · #11 17-10-2010, 01:36 AM

Quote:

Originally Posted by Max Vondel

with a basic 25mm kellner(remember that name!) eyepiece.

Yep! The key here is that the eyepiece should not have any type of 'glue' to bond any of the various elements to another. The heat of the collected solar light will damage this glue, killing the eyepiece.

Kellner, Huygens & Ramsden are cheap eyepieces, ususally even without coatings, or only basic coatings and few elements forming them, from two to three, and all air spaced. These designs are probably best for solar projection.

I have a couple of nasty Huygens eyepieces just for this purpose.

I'd be careful about how large an apeture you use too. Even the Baader film instructions advocate making a mask to cover the scope with only a 50mm to 60mm opening as the maximum apeture, regardless of the size of the scope. With projection, I wouldn't exceed the apeture by more than 5". Even simple eyepieces can be killed by the amount of heat going through them. Even 4" is plenty.

You can make a simple mask from a piece of stout 'corrugated' cardboard from a box pinched from a fruit and vegie shop. This will give you the protection of three layers of good thick card to block the sun and heat.

circumpolar (Matt) · #12 21-10-2010, 06:33 PM

All good advice.
If your projected image is too small and bright just move your projection screen further back from the eyepiece. This will reduce brightness and inlarge the image.

You may find that you can now find focus.

Merlin66 (Ken) · #13 21-10-2010, 06:40 PM

Hmmm
I use full aperture Baader Solar film filters on my 4", C9.25 and 12" scopes.
Unless the seeing conditions are absolutely excellent, the 4" shows as much as any of the others...

Geoff45 (Geoff) · #14 25-10-2010, 02:42 PM

I used to do it many years ago as a teenager with a six inch reflector. Never had a problem. I think six inches is about the limit for this sort of thing if you don't want to fry your eyepiece--use a cheap one.
Geoff

Steffen · #15 25-10-2010, 04:43 PM

I too used to do a fair bit of solar projection as a teenager. School telescopes in those days came with a solar projection screen attachment to make this easy and straightforward. The scope I built myself from a Carl Zeiss kit (55mm achromat, eyepiece holder and two Huygens eyepieces) didn't have that but it was easy enough to rig up a screen. Being Huygens the eyepieces weren't as much in danger of being damaged, but I don't remember them getting hot anyway.

Projection was considered the safest method of showing the Sun and solar eclipses to kids, guests etc. We didn't have access to solar filters back then and welders glasses or soot blackened glass were the only other options (inferior of course from a safety point of view).

Cheers
Steffen.

jasongrover (Jason Grover) · #16 09-01-2013, 08:39 PM

I believe it is neither safe for you and your eyes nor for your scope. Better take care.

____________________
projection screen fabric

Chif (Andrew) · #17 09-01-2013, 09:10 PM

Quote:

Originally Posted by Merlin66

Definately the Baader Solar Film is the way to go!
110% safe (when applied properly) and it will allow you to see the surface detail better.
Don't worry, the new solar cycle is just beginning... in the next few months you'll start to see more and more activity. Now is the time to practise.

This! I got some the other day and have been using it with my DOB. It's very interesting. I could see a few sunspots, and even more after taking some pictures.

pgc hunter · #18 10-01-2013, 01:38 AM

Solar projection is safe. Use a long focal length eyepiece, no need for high magnification on the sun. Something like a cheap 25 or 30mm Kellner or Plossl eyepiece will reveal sunspots and other features, and you can enjoy the projected image without having to reposition the scope every few seconds.

However, when projecting, you still have to be careful. Never, ever look directly down at your eyepiece. Use your telescope's shadow to find the sun, when the tube shadow looks like a circle/is at minimum, the sun will be shining out the eyepiece. Also you should keep the finder covered to avoid damaging it or worse yet burn your self or anything else.

When I project, I always stand well away from the eyepiece and make sure never to look directly into it or at it. I always keep my line of sight well away from the eyepiece.

Holding the projection screen/paper or whatever you are using at least 30cm from the eyepiece will yield good results. Too close and all you'll see is a blinding image with no features. You can use the telescopes focuser to get the image into focus as far from the eyepiece as you want until the image becomes too dim to see. Holding the projection screen 30-50cm from the eyepiece yields the best results IMO.