Sunday morning fun in CaK with the C11

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Montana
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Sunday morning fun in CaK with the C11

Post by Montana »

Yesterday (30th August) the sky was beautiful and blue and my C11 was pre-cooled in the greenhouse overnight. I was set up by 9am and waited for the Sun to drop its rays onto the C11. A big thank you first of all to Alfred for helping me such a lot, his encouragement and tinkering enabled me to use the 2.5x Powermate with the aid of a Skybender from Apollo and everything worked a treat.

All were taken with a C11 / ARIES ERF / 2.5x powermate + Skybender / ASI174 / Lunt CaK module. The C11 was stopped down to 18cm (7") best results and I also tried at 23.5cm (9.75") but the images were not as good. All diameters are in Flickr in the description box. I feel that this is about the best I can do, the seeing was very calm and the video feed very nice indeed but I am still unable to stack very fine detail like Valery and Alfred. My resolution in CaK and Halpha always seems to be about the same. I can get finer detail in WL. Maybe my collimation is not accurate enough or I very much need to visit St Véran with Christian V for a thorough test :)

ImageSun_081704_30_08_2020_a by Alexandra Hart, on Flickr

ImageSun_081438_30_08_2020_a by Alexandra Hart, on Flickr

ImageSun_084959_30_08_2020_a by Alexandra Hart, on Flickr

ImageSun_084959_30_08_2020_colour by Alexandra Hart, on Flickr

ImageSun_082430_30_08_2020_a by Alexandra Hart, on Flickr

ImageSun_082306_30_08_2020_a by Alexandra Hart, on Flickr

I then set up the Solarscope DSF100 and just about managed a full disc and some prominences before clouds rolled in for good. (all details in Flickr and best viewed there with the magnifier)

Image2020-08-30 Halpha full disc by Alexandra Hart, on Flickr

Image2020-08-30 Halpha full disc with proms by Alexandra Hart, on Flickr

and some sunsets from yesterday evening to finish.

ImageSunset 30th August 2020 by Alexandra Hart, on Flickr

ImageSunset 30th August 2020 by Alexandra Hart, on Flickr

First time I have seen the Sun properly for a couple of weeks now.

Alexandra


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Re: Sunday morning fun in CaK with the C11

Post by ffellah »

Looks like you had a very good session with the C11. The full disks with the Solarscope are excellent.

Franco :seesaw


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Re: Sunday morning fun in CaK with the C11

Post by marktownley »

Super shots Alexandra! Yesterdays skies were very blue first thing. One of the reasons you likely get higher detail in WL compared to Ha or CaK is that the scope will have a much higher strehl value at 540nm.


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Re: Sunday morning fun in CaK with the C11

Post by Valery »

Montana wrote: Mon Aug 31, 2020 10:30 am
All were taken with a C11 / ARIES ERF / 2.5x powermate + Skybender / ASI174 / Lunt CaK module. The C11 was stopped down to 18cm (7") best results and I also tried at 23.5cm (9.75") but the images were not as good. All diameters are in Flickr in the description box. I feel that this is about the best I can do, the seeing was very calm and the video feed very nice indeed but I am still unable to stack very fine detail like Valery and Alfred. My resolution in CaK and Halpha always seems to be about the same. I can get finer detail in WL. Maybe my collimation is not accurate enough or I very much need to visit St Véran with Christian V for a thorough test :)

Alexandra,

All my best images of the Sun in UV, at 393,4nm and at G-band were taken with C11 at it's full aperture and withont special corrective optics.
Just TV PM 2.5x and 4x. Mostly with 4x.

You, of couse, need to check (by a star test) the collimation of your telescope. Even slight coma will dramatically worsen the images.
My scope was permanently installed under the SkyShed dome. Despite this, I still checked the collimation time to time and if necessary correct it to a perfect star test.

If your scope is about null corrected in a green light, then do not go lower than 220mm aperture stop. No gain, but will decrease the resolution and contrast. At 220mm aperture C11 has diffraction limited quality - about 0.8 Strehl at 393nm.


Valery


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Re: Sunday morning fun in CaK with the C11

Post by LTHB »

I can only agree with what has been said already: The full disks are excellent: tack sharp, with tiny detail and extremely even! The serene and calm sunsets are very nice, and I also like the CaK shots as they are!

But then you are right: IF looked at at full resolution the CaK images are slightly soft, but I'd suspect that the explanation may simply be the seeing. With a 2.5x barlow the C11 and the ASI174 should give a resolution of about 0.17'' per pixel. So if your seeing is 1.0-1.2'' (which is VERY good seeing for my location) the finest resolvable details are covering 6 to 7 pixels, at 1.5-1.8'' seeing (which is good for my location) around 9 to 10 pixels, i.e. the images would be a bit oversampled. For a sampling rate of 3 pixels for the finest details you'd have to have seeing values of around 0.5'' (which I have had maybe three times in my lifetime). My experience with Autostakkert is that it cannot really handle oversampled solar images well; I'd be glad if someone told me a trick to do it better, but every time I fed an oversampled, but otherwise not that bad video into Autostakkert, the result was more or less unusable mush.

For me the best strategy to get usable CaK images so far has been to adjust the focal length and/or pixel size to the seeing, so that the sampling is about two or three pixels per finest detail that the seeing allows, and an SSM helps a lot with this. (Another thing that helped with higher resolution CaK imaging for my setup is to take care of thermal problems as far as possible, but that is another story...)

Kind regards,

Frank


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Re: Sunday morning fun in CaK with the C11

Post by Montana »

Thanks guys, I was really pleased with these images, they were my best so far :hamster:
Frank, I quite agree, I feel my biggest downfall is the stacking, I can have a lovely video and the stack is nothing like as good as the best single frame ;) I am sure I am missing a trick somewhere.

Alexandra


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Re: Sunday morning fun in CaK with the C11

Post by JochenM »

Excellent results, Alexandra. Good to see that you're improving!

Very nice sunset as well.


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Re: Sunday morning fun in CaK with the C11

Post by DeepSolar64 »

Alexandra,
While I like all your images here I love the Ha full discs. The detail in them is so sharp. Superb! So much more than I can pick out visually. I was most impressed by the depth and detail in the filaments. I certainly hope you can get more clear sunny skies!

James


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Re: Sunday morning fun in CaK with the C11

Post by Carbon60 »

Beautiful images, Alexandra; all of them, but those Ca II K images are sublime. Stunning.

I wish my RCT could operate as well as your C11 at that wavelength. Last time I tried it was just a blurred mess, so either I’m doing something wrong, or it simply isn’t up to the job. Your images have inspired me to have another go, though.

Stu.


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