Welding filter good for solar obs thru telescope?

Hello I went to the hardware store today and I saw some welding helmet, the welding filter lens replacement its sold separately for around half a dollar each, could I make a custom solar filter out of 4 of this filters glued together with my 8 inch lxd 55 telescope¡?, or am I risking my eyes?

Thanks and clear skies.

Ricardo R. Amador

You're risking both your scope and your eyes if you use anything other than a quality filter that covers the scope's aperture. You don't want 8inches of aperture gathering full sunlight, period, end of story.

#14 welder's glass is the one you need (that's number fourteen...I have to spell it out just to make sure that nobody reads the number wrong and buys something that is unsafe for solar observation). However, there are a few problems with using welder's glass as a solar filter:

1) All solar filters MUST be placed in front of the aperture, not behind the eyepiece. Welder's filters come in a few standard sizes, the most common being 4.25" x 2" and 4.25" x 3.25". You will need a sheet at least 9" square to properly cover the entire aperture of your scope. Because welders don't use helmets with 9" viewing portals, finding such a large sheet of welder's glass is going to be quite difficult.

2) You need a good way of mounting the glass securely over the aperture of your scope. It's not going to be easy without a fair bit of work.

3) Welder's glass imparts a green tint to the image. Needless to say, that tint will be rather unnatural.

4) The optical quality of welder's glass tends to be fairly low, simply because welding doesn't demand high levels of correction and resolution. Chances are the image will be somewhat distorted because of this.

I don't know what the cost of the welder's helmet is, but I suspect that it's more than the cost of a sheet of Baader film (~$30). Using the directions that come with the film it's easy to make your own filter. Go to http://www.astro-physics.com/ for details. Be sure to get the 'visual' quality solar film, not the 'photographic' type.

Jim

Ricardo ... Viewing the closest star is indeed fun, but it can also be dangerous. Whatever you make needs to cover the entire end of the scope ( not the eyepiece ) and should fit very snug so it can't blow or fall off. Here's a link that shows a good homemade solar filter. It is safe and very low in cost.

http://www.starcrwzr.com/filter.htm