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Nothing to see, but loads to see....


Stu
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Observing the sun in white light yesterday, it struck me that whilst the disk was basically blank, there was a huge amount of detail to see still, enough to keep me observing for quite long periods each time when the seeing was good.

Many people think white light observing is very boring unless there is an active region visible. I suspect that is because either the setup they have is not optimised or just that they have not trained their eye to see the detail that is there.

Yesterday for example, there was a lovely patch of faculae which has appeared over night around the limb, and at least one other small area elsewhere on the limb. Outside that, the granulation visible when the seeing calmed was quite stunning. At high power, and by high power I mean x200, the tiny granulation cells started to open up, being around 1 to 2 arc seconds in size.

Quite often, when I first look, I struggle to see anything as my eye has not picked up the focus point properly, and it can take a few minutes to get there. I normally focus on the limb, then on any feature such as faculae, then start looking in the centre of the disk. Sometimes I can see the granulation is there but my eye is still not catching it properly, so I find that panning the scope then gives enough movement for it to suddenly snap into focus.

Focus is another key point. Accurate focussing is essential; I always refocus every time I come back to the scope and frequently during each session just to make sure I am spot on. A fraction of a turn of the fine focuser is rough to make a difference and by fraction I mean 1/10 of a turn or so. It really does affect what you see.

I find that the granulation is most vivid in the centre areas of the disk, presumably because that is where you are looking directly into the cells and the contrast is best. Towards the limb the granulation tails off but limb darkening means that this area is where you will see faculae at its best. I find that I perceive the detail in the central area of my vision, beyond that it tails off so wide fields of view aren’t necessary.

With the excellent seeing yesterday, I was seeing amazing detail. Everywhere I looked, I saw different patterns, and in various places there were denser, more complex areas with tight knots, almost approaching small spots but not as dark, along with lighter lanes and in one case an oval of light with a darker centre. At one point I spent fifteen minutes looking at the same spot. It took effort but I could definitely see changes in the patterns during that time as most cells only last about ten to twenty minutes.

My kit has developed over the years, and I’ve tried many different combinations. What I have now is very convenient to use, portable but also gives a quality of image that keeps me happy. I use a Tak FC100DC with FeatherTouch focuser. I then use a Baader CoolWedge with Continuum filter, Baader Zeiss Mark IV binoviewers with a x1.7 GPC and Zeiss 25mm Orthos (converted microscope eyepieces which are very sharp, have excellent transmission, low scatter and good eye relief). To get to high power, I add an AP Barcon and then add extension tubes via Quickchanger fittings when I want higher power. It is an unusual setup which I don’t suggest replicating but it avoids changing eyepieces and does work for me. I certainly find that barlowing long focal length eyepieces works better than trying native short focal lengths, the images merge more easily and the eyepieces generally have bigger exit lenses and better eye relief.

I use binoviewers to mitigate  the floaters which inevitably happen with eyes my age (50) and high powers with a 4” scope and a bright object.

A good setup will cost money of course, but doesn’t have to cost a fortune. I do find the Baader CoolWedge to be a notch above the Lunt wedge, particularly at high powers, but that said the Lunt is still excellent. I don’t have experience of the other options out there. I think the scope is likely to make the biggest difference though and here I would recommend something with a well figured objective, with excellent correction for spherical aberration as poor performance here can really kill the detail. Somewhere around 100 to 120mm is probably optimum to make the best of our normal seeing conditions. Larger will definitely show more due to the additional resolution under good conditions but it is likely that they will be affected by poor seeing much more often. Fast achros should be avoided I think as they often suffer with this. That said I suspect the 152mm f5.9 scopes perform pretty well as they are well corrected, but in the 4” category something like a good TAL 100 or Lyra Optics 102mm f11 (or clone) would be a very good choice. The ubiquitous 120ED is also an excellent option for solar, being at the upper end of the optimum aperture and with very fine optics which will deliver excellent results. Inwards focus if using binoviewers is something to be mindful of, but is likely to be less of an issue because you often use a Barlow to get to the powers necessary. A dual speed focuser is highly recommended as mentioned earlier.

In terms of binoviewers, I have found the TS Optics units or similar spec clones are very good quality, with self centring eyepiece holders and individual focusing on each eye. Careful balancing of the focus for each eye is another area that makes a difference to the detail seen. My Mark IVs do not have this feature but the eyepieces do so I can still easily achieve excellent balanced focus between the two. The Mark IVs do have very tight tolerance on the eyepiece holders so merging of the images is never a problem. Careful setting of the interpupilliary distance is also very important to make sure both eyes are recieving full illumination. Repeating wink of alternate eyes when in position shows whether this as correct; both views should look equally well and evenly illuminated.

In terms of eyepieces, there is plenty of choice out there but I would think that some of the 12.5 or 18mm orthos out there would be a good option; simple lens designs with sharp optics and low scatter are what you want to look for.

Finally, a good solid tracking mount is very handy to give a stable view and allow you to concentrate on pulling out the detail. I normally use my Vixen GP with dual axis drives. Accurately polar aligned it with track the sun all day without problem and is quick and simple to use. I also use an adjustable observing chair so I can get comfy for fifteen or twenty minute sessions and to be able to relax.

Gosh, this has turned into a bit of a monster post, I kept thinking of more to add. Well done if you have got this far, and I hope it is of some use. There are many ways to skin the solar cat though so if you have a setup which works well already, all the better. As the Sun slowly wakes up I hope we all get some amazing views of lovely Active Regions over the coming years. If your setup shows granulation well, then the detail which can be perceived in the ARs is amazing, often rivalling many images I find.

Solar White Light observing; it’s the future I tell you 🤣🤣👍👍.

Stu

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Stu what an excellent write-up and as you say the Sun might be 'blank' but there is lots to observe with the correct equipment. As I told you privately I so regret selling my 4" Astro Tech frac and Lunt HW but I want to return to more WL observing in the near future. Currently I am using a Skywatcher 150P with a front filter which gives an orange Sun which is okay (ish) but I want to obtain a better view.

 

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2 minutes ago, Merlin66 said:

Good seeing certainly helps.....

As you say Ken, in fact it’s probably the biggest factor which is out of our control. Even a great setup is completely floored when the seeing doesn’t co-operate. The only way to counter it is to observe as often as possible so as to try to catch the best times.

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15 minutes ago, Mark at Beaufort said:

Stu what an excellent write-up and as you say the Sun might be 'blank' but there is lots to observe with the correct equipment. As I told you privately I so regret selling my 4" Astro Tech frac and Lunt HW but I want to return to more WL observing in the near future. Currently I am using a Skywatcher 150P with a front filter which gives an orange Sun which is okay (ish) but I want to obtain a better view.

 

Thank you Mark 😀

I do hope you manage to pick up another nice refractor as I know you enjoyed your last one. Not sure if one of the f11s would do the trick? Perhaps harder to mount but would give lovely views. A 4” ED again would be ideal though.

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Great post Stu,

If I was not already sold on WL Solar, then I would be wanting to try now.

All I can add to those reading this thread, who have not tried, get the basic kit or borrow it and have a try.

I find WL most engaging and it gets me sketching each time, so hones my observing skills.

The best bit you go out in the daylight and warmth, what’s to no like about that.

 

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Thanks for that full and very interesting post regarding your observations in WL. Recently I have been tending to concentrate mainly on Ha observing but before I had the Lunt scope my experiences were much like your own.  Seeing the fine detail of granulation does take time, dedication and experience but is well worth the effort. In my case I found that using a solar continuum filter was essential. I just could not get the same results with a polarising filter. 
Thanks again Stu for reminding me of what I have been missing and I will set up both scopes from now on.

John

 

 

 

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9 minutes ago, John said:

Great piece Stu - thanks for that :smiley:

I'm motivated to spend more time with my Tak 100 and Lunt HW over the coming weeks and months now.

That setup will certainly give you excellent results John I’m sure. It’s just a different way of observing and training your eye to see the detail that’s there I guess.

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  • 1 year later...
On 26/02/2022 at 17:46, Sunshine said:

This is a great writeup for anyone thinking about a solar wedge, I will seriously consider a Baader wedge.

It is a fantastic post. I have two 4 inch achromatic refractors and a 6 inch one too. When the sun is higher and the weather cooperates I hope to give the 6 inch its maiden voyage with the Altair wedge I have. Has some nice viewing with the 4 inchers last spring.

I was scared at first to try because of the potential dangers of pointing a telescope at the sun and putting eye to eyepiece. But I am glad I did! 

I've tried all my filters, an OIII giving sharp definition in my humble opinion, very similar to the solar continuum filter.

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1 hour ago, reezeh said:

I've tried all my filters, an OIII giving sharp definition in my humble opinion, very similar to the solar continuum filter.

I’ve used an OIII filter before and agree that they do work pretty well. It’s effectively doing a similar thing, reducing down to a very narrow band pass which tightens up the image and helps the detail.

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That looks like my setup, white light and ha at the same time.

20210918_170327.thumb.jpg.7d6748faa439eb1c99d302386c8cafb7.jpg really like to map ha features to white. The Herschel prism is a Russian one. Can’t remember the name of but works very well. 

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54 minutes ago, skybadger said:

That looks like my setup, white light and ha at the same time.

20210918_170327.thumb.jpg.7d6748faa439eb1c99d302386c8cafb7.jpg really like to map ha features to white. The Herschel prism is a Russian one. Can’t remember the name of but works very well. 

Yep, it’s one of my favourite things to do. Nice setup, what’s the white light scope, I don’t recognise it?

I do like to compare features, but the orientation is different between white light and PST so it gets confusing! One day I would like to change my PST mod to a Stage Two (getting rid of the black box), then the orientation should be the same I think.

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Just now, skybadger said:

It's a 6* cassegrain. Unknown make.

Makes the solar image nice and bright and big with no transmissive optics 

Thanks! The secondary obviously copes with the heat ok??

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I really love white light solar observations too. Nothing wrong with that. Granulation is fantastic to observe as well as the changes in spot development over day's. Images taken with just an 80mm ed refractor and Lunt wedge with zwo ASI 178mm camera. What's not to like. 

20200706-092716UTellabryant-AR2835-WL-col.jpg

20200706-093139UT-UnnamedAR-WL-1-1 -col.jpg

20210630-100207UTellabryant-WL-AR-col.jpg

20210630-100207UTellabryant-WL-AR-1.jpg

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12 minutes ago, skybadger said:

Yeah no probs, compared to say a transmissive lump of glass ?

🤣🤣. Well, I always thought the problem was that the heat was more concentrated at that point so you risked the secondary overheating, coming unglued etc. clearly not a problem on your scope 👍

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On 26/02/2022 at 11:46, Sunshine said:

This is a great writeup for anyone thinking about a solar wedge, I will seriously consider a Baader wedge.

Buy one IMHO.

Used one for years and are considered the best out there. Your 100mm Triplet will give extremely good views. I've found that going up to 120mm makes observing much more seeing sensitive. My 90mm is much more flexible in regards to this. That being said, when conditions allow, the extra aperture really makes a difference.

You might be shocked at the views with your scope and a Baader Cool Wedge.

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