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Welder's glass, moon filter, Dob, eclipse!

6 replies to this topic

#1 provels

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Posted 07 April 2024 - 09:01 AM

First post!  Whee!

 

I know there are better ways to approach this.  But I have a 6" Dob I built about 20 years ago that I'd like to pull out for tomorrow.  I bought some shade 14 welder's glass and cobbled together what amounts to a moon filter made from paper coated foam board with a 3" hole covered by the glass.  I plan to use an eyepiece that is about 25mm (been so long, I forget). Not that I expect this to work particularly well, but it should at least be safe, right?  Thanks for reading and any responses.

 

Pete

 

 



#2 sbsbbugsy

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Posted 07 April 2024 - 09:11 AM

The filter MUST cover the FRONT of the scope. If it is at the eyepiece, it will be exposed to the concentrated light from the optical train and could crack or melt, depending on the type of material it is made from. At the very least, the eyepiece will become too hot to put your eye near.


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#3 AsleepAtTheScope

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Posted 07 April 2024 - 09:27 AM

Hold the whole thing (filter) up to the Sun and be sure there's no light coming through the foam board.



#4 provels

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Posted 07 April 2024 - 10:15 AM

Here are some quick pictures of the affair on OneDrive.

 

https://1drv.ms/f/s!...K73CXA?e=jtR10A

 

1 .  The naked eye view through the glass taken with phone.

2.   The project installed (will be fastened with a wing nut).

3.   The spider.

4,5. Shots of the "moon filter" (plastic lid) and the project, front and back.

 

Glass is held on with Gorilla tape, foam sheet overlaps tube by about 1/2", backed with thin closed-cell foam sheet, and sprayed black.

 

What think?  

 

Pete


Edited by provels, 07 April 2024 - 10:15 AM.


#5 AsleepAtTheScope

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Posted 07 April 2024 - 11:14 AM

You're going to have to decide for yourself. #14 welder's glass is supposed to be safe as long as there isn't any sunlight leaking through somewhere, including any UV or IR. If you're saying to yourself, "How do I tell if there's any UV or IR leaking?", then I'd say that's a really good question.


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#6 provels

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Posted 08 April 2024 - 11:05 AM

If I see some success, I'll post a couple shots.  Maybe from the ER!

 

EDIT - Scope and Photography were both a washout.  But the welder's glass worked great in hand.  I'll try again in '44 if I live.


Edited by provels, 08 April 2024 - 05:24 PM.


#7 lajoswinkler

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Posted 08 April 2024 - 11:20 AM

If you're going to use the welding filter at the telescope objective aperture, and no unshielded light is passed, this will work reasonably well. Having a variable polarizer attached to the ocular lens can be beneficial to adjust the brightness if it feels too bright.

 

DIN13 and DIN14 standards for welding filters are really dark and are designed to also strongly attenuate ultraviolet and infrared radiation. Afterall, they're electrowelding filters for high current arcs (hundreds of amperes, even over kiloampere) which radiate strongly in those parts of the EM spectrum.

The only problem I can see here is if the filter slips away due to its weight. Be very careful about that. You have to make sure it is sturdy and sticks well. If it falls off, it's a pulse of eyeball-cooking rays...

 

Also, don't expect pristine details of the photosphere. Welding filters are far from optically correct elements. They are thick and induce distortions.


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