White light solar observing

[astro1965 (Nick)]

Hi all,I currently have a 12 inch dob and was thinking about doing
some solar observations.O.k heres the thing,just how safe is observing the sun with some of these solar filters(paper ones ) that are out there and can anyone recommend the best brand of white light solar filter?I just feel nervous about looking at the sun,with these filters.Thanks all,Nick.

[julianh72 (Julian)]

I don't know of any paper solar filters, but there are a couple of types of full-aperture solar film filters ("Mylar" film) that you can buy, as well as glass filters, which are generally a bit more expensive. Some give a white image, some give a yellow / orange image, but I think they are pretty much the same in other respects.

You can buy ready-made solar film filters ready-mounted to fit your scope, or you can buy the loose film sheet, and make your own holder to mount it onto the scope. E.g. see http://www.ozscopes.com.au/Viewing-t...For-Telescopes (It will probably be a lot cheaper to make your own for a 12" Dob.)

Don't expect to see any prominences or flares with one of these, but you will see sunspots and granulation. They're perfectly safe to use as long as you follow a few key safety rules:

Check the filter for scratches or pinholes before fitting it to the scope. Discard it if it has any damage.

Fit the filter to the scope BEFORE pointing it at the Sun.

Make sure it is secure, so it can't be dislodged by someone bumping it or a gust of wind.

Keep your finder-scope capped (or buy / make a solar filter for it as well.)

Don't leave the telescope unattended in case inquisitive kids take the solar filter off.

If you have an open-truss telescope, consider putting a shroud around the truss, to make 100% sure that unfiltered sunlight can't hit the mirror and reflect up towards the secondary.

[astro1965 (Nick)]

Thanks for the info Julian ,I think I will probably make a solar film filter to fit my 12 inch dob and check like crazy the filter for holes or tears.Hopefully I will get some good views of the sun.thanks Nick.

[nasapete (Pete)]

Hey Nick,

White light solar viewing is a great and inexpensive way to get into solar viewing, for myself I purchased a pre made filter that goes into the end of my tube, and are more than safe to use, make sure you buy a quality one, things to remember though, check it by holding it up and making sure there are no holes in it, though they look rather fragile, they are still quite tough, also I have heard people not taking off the finder scope from their main scope and obviously getting burnt that way, and make sure you don't buy one of those solar filters that work at the eyepiece like the thread on filters, I think they were banned but occasionally they do show up, as the tube will heat up and the glass in them will crack, if you can't find the pre made ones at all that go on the front of the tube you can make your own from baader solar filter film.

Clear skies to you

[nasapete (Pete)]

And I just read someone else had already replied so my apologies for repeating anything then

[Tinderboxsky (Steve)]

Originally Posted by astro1965

Thanks for the info Julian ,I think I will probably make a solar film filter to fit my 12 inch dob and check like crazy the filter for holes or tears.Hopefully I will get some good views of the sun.thanks Nick.

Nick, the Baadar film is surprisingly tough. Normal careful handling is not a problem. Certainly check before using as others have said.
I have made three filters now for apertures up to 140mm out of good quality cardboard, tape and glue. That is all that is needed and they work well.
I would not make a 12" filter. The image will be too bright to look at comfortably. Even 8" ones are overly bright. In your case I would be making an off axis 4 to 5 inch filter. This is all the aperture you need for the Sun and will deliver an excellent, comfortable image. You will also have the advantage of no central obstruction. In any event the standard sheets would not cover 12".
Let us know how you go.

Steve

[julianh72 (Julian)]

Originally Posted by Tinderboxsky

I would not make a 12" filter. The image will be too bright to look at comfortably. Even 8" ones are overly bright. In your case I would be making an off axis 4 to 5 inch filter. This is all the aperture you need for the Sun and will deliver an excellent, comfortable image. You will also have the advantage of no central obstruction. In any event the standard sheets would not cover 12".

You can buy Thousand Oaks solar film (gives a natural orange image) on eBay in sheets up to 12" x 12" for about $45 (including postage). The biggest full-aperture filter I have made is for my 200 mm SCT, and it is very comfortable for viewing the Sun. (And I made a couple of smaller filters for my finderscope, binoculars and a 90 mm Mak with the corner off-cuts.)

But yes, I agree that a 5" off-axis filter would be fine (and cheaper).

[astro1965 (Nick)]

Thanks guys for all that info,I never thought that the view thru a 12 inch dob would be so bright,so yeah, an off axis filter is the way to go.As soon as I get some spare time,I will start getting the materials together for the filter and give it a go.Nick.