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PaulM

Viewing the sun directly through my 12" dob

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Hi,

Firstly apologies for the question as it would have been asked a lot previously in this part of the forum but I don't want to just research this and get things wrong and subsequently damage my eyes and\or equipment

In order to observe the sun directly through the EP safely through my 12" dob what do I need? and can I use my existing EPs which are listed in my signature

many thanks

 

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your going to need a filter covering your open end or if you have a small cap in your large cap you could put a filter on that but the full option would be the better. badder solar film is great for making your own. you will beable to use your eps as useal. charl. ps heres the film https://www.firstlightoptics.com/solar-filters/baader-astrosolar-safety-film-nd-50.html you can also get glass filter but there pricey and at 12inch I think you may have to reduce the size because I don't think the film is big enough or maybe thay do bigger sizes.

Edited by xtreemchaos

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4 minutes ago, xtreemchaos said:

your going to need a filter covering your open end or if you have a small cap in your large cap you could put a filter on that but the full option would be the better. badder solar film is great for making your own. you will beable to use your eps as useal. charl. ps heres the film https://www.firstlightoptics.com/solar-filters/baader-astrosolar-safety-film-nd-50.html

Thanks

I assume this will do the equivalent? https://www.firstlightoptics.com/solar-filters/astrozap-baader-solar-filter.html which states at the bottom 

NOTE: Not suitable for use with open-tube telescopes, like 'truss' Dobsonians. 

As I have an astrozap light shroud I'm ok?

 

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yes that would be great, and the shroud is a must or all you will see is light coming in from the opening. charl.

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I would seriously question whether a 12" Dob is the best scope to use.  Given the heat shimmer usually caused by daytime sun, it is unlikely to offer any significant improvement in resolution over a 4".   A full-aperture solar filter for a 12" will be expensive.   And in the event of something going wrong, a 12" will make a much better welding torch than a 4". 😥

It would be safer to use a small filter over the 2" hole in your tube cap, even if the performance is not great.  Or buy a small telescope for the purpose.

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16 minutes ago, Cosmic Geoff said:

I would seriously question whether a 12" Dob is the best scope to use.  Given the heat shimmer usually caused by daytime sun, it is unlikely to offer any significant improvement in resolution over a 4".   A full-aperture solar filter for a 12" will be expensive.   And in the event of something going wrong, a 12" will make a much better welding torch than a 4". 😥

It would be safer to use a small filter over the 2" hole in your tube cap, even if the performance is not great.  Or buy a small telescope for the purpose.

That confirms my thinking somewhat wrong tool for the job !

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Also, if you want multi-inch resolution but not the full aperture, consider fabricating a 12" cover with 2 holes, say 8-10" apart?

Magnus

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I must agree a frac would be a much better tool, something from 80mm to 120mm f5 to f7.5, but you would still get good views with a newt but as said not ideal. charl.

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1 hour ago, Cosmic Geoff said:

I would seriously question whether a 12" Dob is the best scope to use.  Given the heat shimmer usually caused by daytime sun, it is unlikely to offer any significant improvement in resolution over a 4".   A full-aperture solar filter for a 12" will be expensive.   And in the event of something going wrong, a 12" will make a much better welding torch than a 4". 😥

It would be safer to use a small filter over the 2" hole in your tube cap, even if the performance is not great.  Or buy a small telescope for the purpose.

I do use a 12" full-aperture filter so this is experience talking. I'll answer those points one by one.

Heat shimmer is vastly offset by increased resolution; my 5" Schmidt-Cass does not compete. The 50cm wide Baader film is not expensive (45€), and after making the 12" filter I had enough left for several others.

https://www.teleskop-express.de/shop/product_info.php/info/p545_Baader-AstroSolar-Filterfolie---Visuell---50-cm-x-49-cm--fuer-Sonnenbeobachtung.html

A glass filter would cost a lot but would be very heavy and not well polished because a glass window made to the same standards as the scope's mirrors is not marketable. Glass filters are low-power only, Baader film can take high power.

Safety measures and solar danger are the same regardless of aperture.

And finally, who wants to downgrade a 12" scope to a 2" scope? The hole in newtonian caps is there only by tradition, and never has the proper diameter to be an off-axis mask, which could be a good solar solution. I made a 115mm off-axis nighttime mask for my dob; that could be a good aperture for a solar filter, but not 50mm.

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1 hour ago, Captain Magenta said:

Also, if you want multi-inch resolution but not the full aperture, consider fabricating a 12" cover with 2 holes, say 8-10" apart?

Magnus

Many people hoped to pull that trick but sadly, it doesn't work. Each sub-scope would look through different turbulent air cells so their images wouldn't match. The view would be disturbed by turbulence anyway and fainter, to boot.

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Looks like a well made filter! I bet the detail is amazing. even more so with this.....

1070_SolarObs_full.jpg

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30 minutes ago, Ben the Ignorant said:

I do use a 12" full-aperture filter so this is experience talking. I'll answer those points one by one.

Heat shimmer is vastly offset by increased resolution; my 5" Schmidt-Cass does not compete. The 50cm wide Baader film is not expensive (45€), and after making the 12" filter I had enough left for several others.

https://www.teleskop-express.de/shop/product_info.php/info/p545_Baader-AstroSolar-Filterfolie---Visuell---50-cm-x-49-cm--fuer-Sonnenbeobachtung.html

A glass filter would cost a lot but would be very heavy and not well polished because a glass window made to the same standards as the scope's mirrors is not marketable. Glass filters are low-power only, Baader film can take high power.

Safety measures and solar danger are the same regardless of aperture.

And finally, who wants to downgrade a 12" scope to a 2" scope? The hole in newtonian caps is there only by tradition, and never has the proper diameter to be an off-axis mask, which could be a good solar solution. I made a 115mm off-axis nighttime mask for my dob; that could be a good aperture for a solar filter, but not 50mm.

Thank you for this and the link to your thread

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8 hours ago, Moonshane said:

Looks like a well made filter! I bet the detail is amazing. even more so with this.....

1070_SolarObs_full.jpg

I guess with this high of resolution one can observe the Sun very close to the horizon as pictured, interesting. 

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On that picture you can see the secondary vanes rubbing against the filter. That's not good for the filter.

 

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1 hour ago, skybadger said:

On that picture you can see the secondary vanes rubbing against the filter. That's not good for the filter.

 

Nah , those are joints in the filter , it's made from four pieces of Baader film , the 'big' rolls are only 1000 x 500 mm , too small to make the mammoth in one ... :thumbsup:

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22 hours ago, Ben the Ignorant said:

Many people hoped to pull that trick but sadly, it doesn't work. Each sub-scope would look through different turbulent air cells so their images wouldn't match. The view would be disturbed by turbulence anyway and fainter, to boot.

I’m not sure I’m completely convinced by the turbulent cell argument. In principle, extending the baseline ought to work, it’s done all over the world. In non-turbulent conditions I’d expect it to work, except in this case for one thing: with a 1500mm focal length (for my 300p at least) and a 50mm aperture you get a focal ratio of f/30, and at that level I’d intuitively expect diffraction-softening to overcome any resolution benefits

 

edit: in fact, on thinking some more, it's even worse than that. the standard f/30 calculation assumes a refractor set-up, where the aperture-stop is at or within the light cone. In this reflector set-up, the stop is almost a full focal-length in front of the primary mirror, so the diffractions have "done" that much more divergence before the cone even starts.

Edited by Captain Magenta

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I see how that could seem to make sense at first sight, but you have to clarify these notions, Captain Magenta. Extending the baseline is done for interferometry, not for visual, and in non-turbulent conditions you wouldn't need to stop down your scope. Also, reducing the diameter benefits in steadiness, but not in resolution.

You have more usable resolution from a smaller aperture; you'll enjoy almost 100% of the resolution a 2" aperture can show thanks to steadiness, but such a reduced scope can't show much. It's much better to make a maximal diameter (115mm here) off-axis mask for nighttime viewing, and a matching solar filter for the mask.

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2 minutes ago, Ben the Ignorant said:

I see how that could seem to make sense at first sight, but you have to clarify these notions, Captain Magenta. Extending the baseline is done for interferometry, not for visual ...

fair enough ... every day is a school day :)

Magnus

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