Solar Observing with Two Eyes

The sky was clear this morning so I decided to do a little solar observing rather than woodworking.  I'd really like to get the two woodworking projects I am working on finished but I couldn't pass up the clear skies especially since I haven't really done any solar observing yet this year.  

I had a couple of things related to solar observing that I wanted to try so it seemed like a good morning to do some experimenting with astronomy gear.  The weather should be nice for the next few days so I could easily put off the woodworking projects for a day so I could finally get to spend some time observing the sun.

I had a lot of nice success with a larger telescope when using my new binoviewers while viewing the moon, Venus and Mars last night so I wanted to try solar observing with the same binoviewers for solar observing.  Viewing with two eyes provides far less eye strain than viewing with one eye and eye strain is something I have been experiencing lately.  

Last night I was using my larger Explore Scientific 102mm APO refractor and that worked well with the binoviewers but I have a smaller telescope that I often use for solar observing so I wanted to try a couple of things with that telescope before jumping into using a few other telescopes.  I suspected that getting my smaller Skywatcher ED 72mm refractor to play well with the binoviewer was going to be a problem so I was expecting this to be a morning of trial and error.  This smaller refractor already has very little play when it comes to backfocus and I know that binoviewers require a lot of backfocus so I was expecting problems.  Actually, binoviewers require an additional 100mm of backfocus and most small telescopes do not have that especially this Skywatcher ED 72mm telescope.  

Before dealing with the binoviewer on this small telescope I had another issue I wanted to attempt to resolve first.  I had drawn up a plan for a way to get a slightly wider view through this Skywatcher ED 72mm refractor.  I can just barely fit the full disk of the sun into my view when viewing with my Quark solar filter with this small refractor telescope and I find that to be very uncomfortable.  This Quark is my best solar filter and the one I use the most so it would be nice to get it to work as best as possible.  A slightly wider view would be nice.

To fit the full disk of the sun in your field of view, you need a very small telescope.  The manufacturer of the Quark filter claims that any refractor telescope with a focal length of less than 450mm is fine for viewing the full disk but I disagree.  My small telescope has a focal length of only 420mm and I feel the view is far too tight.  Ideally, I think a telescope with a focal length of less than 400mm is probably a better option for full disk viewing.

Just because I want to see the full disk of the sun doesn't mean that I don't like close-up views of the sun because I definitely do but I like to see the whole disk all at once also just to compare features without having to slew around the whole sun like peeking through a hole.  Viewing the whole disk at once makes it easier to compare features.  This was my goal and I didn't want to have to purchase another telescope just for better full disk solar views.

I drew up a plan using some parts I have for other purposes.  Actually, I drew up a few different plans.  I want a slightly wider view so I chose to try using a 0.8x focal reducer from my Explore Scientific 102mm APO refractor.  This was a longshot since this focal reducer was made for a completely different telescope but I figured I would try it anyway.  

I screwed a UV/IR Cut Filter to the front end of this reducer to cut down on heat buildup.  The sun is highly magnified as it enters through the front object lens assembly so I wanted to knock down most of that heat before the sunlight enters into this reducer.  If the heat isn't knocked down significantly, the heat from the sun could shatter the glass in this reducer.  The UV/IR Cut Filter should work for this purpose.  So, I started with a UV/IR Cut Filter screwed onto the front end of my 0.8x focal reducer.  

I screwed an m42 to m48 adapter onto the reducer (it is actually a thin T-Ring) and then two extension tubes.  The total extension behind the reducer is 65mm.  In order to screw this reducer assembly to my Quark solar filter, I unscrewed the 2 inch nosepiece at the front end of my Quark filter then screwed the reducer assembly to the Quark.  

On the rear end of the Quark, I inserted my 1.25 inch diagonal.  Then I inserted my 40mm Plossl eyepiece into this diagonal.  Now it was time to test this idea.

I pointed the telescope at the sun and then focused.  The sun easily came into focus!  Better yet, both the sun and my field of view were noticeably larger when using this configuration!  There was more space around the sun before my view was obscured by the edge of the field of view so the full disk of the sun was actually a bit larger and fit comfortably within my field of view.  This would work nicely!  Actually, the view using this reducer assembly was far better than without it.  The whole field of view appeared larger and even the sun appeared larger yet I still have plenty of room around the sun to fit in prominences and allow for some drift due to the Earth's rotation.  

That first experiment worked very well so now it was time to try the new binoviewer on this telescope.  I removed the eyepiece and inserted my new binoviewer.  I inserted a pair of 40mm Plossl eyepieces...  focused...  this also came to focus easily!  This was great news!  I was able to easily come to focus even without the use of the 1.6x corrector lens due to the Quark having a 4.3x telecentric lens inside its assembly.  Not needing to use the corrector lens is a big deal. 

The only downside to this whole assembly, especially with the binoviewer hanging off the end of it, is that it is actually slightly too heavy for the stock telescope focuser when the sun is very high in the sky.  The focuser won't hold this amount of weight without creeping outward toward the ground.  I'll have to see if I can adjust the tension on this focuser.  I'd really hate to have to purchase a better focuser.  When the sun was lower in the sky, the focuser held the weight just fine.  Maybe I can tune up and adjust the focuser and that will make enough of a positive difference.  

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EDIT:  I think I resolved the tension issue with some fine tuning and cleaning.  I disassembled the focuser, cleaned it up, reassembled it and then adjusted it properly and it now is better than it has ever been!

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Here, below, is a close-up of the new binoviewer with a pair of 40mm Plossl eyepieces.  So far, this has been a really nice and useful addition to my astronomy gear.

Next, I'll have to try another telescope for solar observing...