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Solar viewing on the cheap

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#1 dadorfman

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Posted 05 March 2021 - 11:13 AM

In the 80's, I bought my first telescope at a flea market for $100, an Edmund 1000mm, 4" newtonian, white metal tube, equatorial mount.  I had fun with it, viewed some Messier objects, and moved up to Coulter Odyssey 10.1".  I kept the smaller scope and loaned it out, spreading the infection to others.  I knew enough not to try solar viewing with the dob, but rigged a solar projection setup of the Edmund using parts for a desk-mounted lamp.  It wasn't pretty by any means, but it did allow me to view sunspots projected onto a piece of white paper.

 

I have an a classic Astroscan that I have been advised not to use for solar projection.  I don't want to spring for an expensive, to me, dedicated scope designed for direct viewing.  What would be an inexpensive way to get pack into solar projection, not direct viewing or imaging?  Would a cheap refracter with an angle view work for my purposes?  Would a small department store scope on a tripod mount work?  I see any number of them on Craigslist.  Would a cheap reflector by better?

 

Thanks in advance for your advice.



#2 Couder

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Posted 05 March 2021 - 11:45 AM

A small refractor will work for solar projection, but I would advise against anything with plastic. I believe many of the sunspot observations are made with a 60MM refractor. 



#3 astro rocketeer

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Posted 05 March 2021 - 12:09 PM

There’s an Orion 70mm White-Light Solar refractor that I’ve read on solarchat.com and others that are excellent and unbeatable for $160. I’ve seen it as low as $100 on eBay I think it was https://www.telescop...cope/118193.uts something to consider.

 

cost much less than a solar edge and all other accessories you need with it too


Edited by astro rocketeer, 05 March 2021 - 12:12 PM.


#4 dadorfman

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Posted 05 March 2021 - 03:28 PM

Here's another thought:  Mount a Celestron EclipSmart Solar Filter - 6” SCT on the Astroscan, held on with velcro.  The Astroscan outer diameter is about 5 1/2", so I would need to fill the gap, maybe with weatherstipping.  At $45.95, I could go for that.  Downside is that Celestron says it is for yellow-light viewing.



#5 dadorfman

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Posted 05 March 2021 - 10:28 PM

I kept looking and found a number of inexpensive scopes with detachable/nondetachable solar filters.  I decided to go with a filter for the Astroscan, a Spectrum Telescope 6" filter for $66.95, sold on Amazon but shipped from Spectrum Telescope.  It fits a tube outer diameter of 5 5/8" to 5 7/8", a tighter fit than the Celestron.  I will report back when it ships. This should give me what I want without adding another telescope to store.  Let us pray.


Edited by dadorfman, 05 March 2021 - 10:28 PM.


#6 dadorfman

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Posted 30 March 2021 - 10:05 PM

Having to return the Spectrum filter.  The lip on the holder is too deep for the Astroscan tube without modification of the holder.  Back to looking!



#7 Napp

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Posted 30 March 2021 - 10:36 PM

You can buy Baader Solar Safety Film for visual and make your own solar filter to fit over the opening of your scope.  Cheap way to have a very good white light solar filter.

 

https://agenaastro.c...et-2459286.html



#8 briansalomon1

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Posted 31 March 2021 - 12:26 PM

You can buy Baader Solar Safety Film for visual and make your own solar filter to fit over the opening of your scope.  Cheap way to have a very good white light solar filter.

 

https://agenaastro.c...et-2459286.html

Solar projection works with a refractor because it's just the objective cell (and eyepiece) bending the light. No focused/concentrated sunlight has to pass through an (expensive) optical lens/element and if you do damage it, an inexpensive eyepiece is easy to replace.

 

With a Newtonian or Schmidt Cassegrain, the optical power of the concentrated sunlight reflecting off the secondary mirror is way higher than the mirror coatings were designed for.

 

So if you use the Baader film, your Astroscan will work fine for direct, white light viewing and your seeing is likely to support a 100mm aperture without too much trouble. The film in the Astroscan will give a better quality view than the projection method without buying another telescope.


Edited by briansalomon1, 31 March 2021 - 02:14 PM.

  • Siderius and viewer like this

#9 connywithay

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Posted 03 April 2021 - 10:25 PM

I would like to try observing the sun. I have two telescopes. A Celestron Powerseeker 70AZ and a HOC 6-5 (Newtonian Reflector 6” f/5). Which one would be the better scope to use? I need to decide which size solar filter to get. Alternately, Celestron makes an inexpensive solar scope. Should I get that instead? Cost would be about the same as the solar filter for either one of my scopes. Does anyone have an opinion on/experience with the Spectrum Full Aperture Glass Solar Filters?

 

Thanks in advance for your advice.



#10 Napp

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Posted 04 April 2021 - 05:58 AM

Baader Solar Safety Film for visual will provide a sharper image than a glass filter and is cheaper if you make your own filter.  It's available at many astronomical retailers.  The link shows instructions on how to build a filter and examples of premade filters.

 

https://astrosolar.com/en/


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#11 dadorfman

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Posted 04 April 2021 - 08:28 PM

I would attempt this DIY project if not for two problems:

 

1.  The front of the focuser and the Telrad base will not allow the narrow lip of a commercial filter assembly, let alone the wider width of the cadboard.

2.  The instructions say to use an adhesive for a permanent mount.  I need to be able to remove the folder for use as a travel scope.  I could use velcro if I could rely on velcro straps not to let in any sunlight.  I have ordered a filter attached with screws to the outside of the OTA and removable for non-solar observing.



#12 Napp

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Posted 05 April 2021 - 01:23 AM

I would attempt this DIY project if not for two problems:

 

1.  The front of the focuser and the Telrad base will not allow the narrow lip of a commercial filter assembly, let alone the wider width of the cadboard.

2.  The instructions say to use an adhesive for a permanent mount.  I need to be able to remove the folder for use as a travel scope.  I could use velcro if I could rely on velcro straps not to let in any sunlight.  I have ordered a filter attached with screws to the outside of the OTA and removable for non-solar observing.

Those certainly don't seem insurmountable.  A simple notch in the ring around the outside of the tube (not the tube opening) should handle the focuser and Telrad.  I'm not sure where in the instructions you saw a recommendation of a permanent mount to the tube.  I suspect you misunderstood the instructions.  I certainly don't know of anyone who has done that as they wouldn't be able to use the scope for observing at night.  Velcro actually works quite well.  Even if the filter is held by screws I would still recommend taping the filter to the tube, especially in outreach situations.  I've personally seen someone swing a scope around with a glass filter like you are buying and seen the filter fall off.



#13 connywithay

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Posted 05 April 2021 - 11:04 AM

Baader Solar Safety Film for visual will provide a sharper image than a glass filter and is cheaper if you make your own filter.  It's available at many astronomical retailers.  The link shows instructions on how to build a filter and examples of premade filters.

 

https://astrosolar.com/en/

That’s very helpful advice. I never would have thought that solar film will deliver sharper images than glass. Thanks for the video, too.




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