CaK – 30th July

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CaK – 30th July

Post by LTHB »

Once again an almost quiet solar surface in CaK, taken yesterday afternoon during a stretch of (for my location) exceptionally good seeing:

Image


A resampled version (150%):
Image


Full sizes here: https://live.staticflickr.com/65535/484 ... 7925_o.jpg https://live.staticflickr.com/65535/484 ... e25f_o.jpg


One thing that struck me when I looked over my pictures from the last weeks: If time and weather allow I usually do a dozen or so videos and pick the best after processing them with Autostakkert. Rather often the first of the sequence of videos of one session proved to be the best, i.e. sharpest and most contrasty, in particular when shooting in CaK.

I suspect that this may be due to some sort of thermal problems with the Mewlon that (more or less) impair the later videos: maybe tube seeing that builds up during a session as more and more energy is absorbed inside the tube. Usually (i.e. at night) the Mewlon doesn‘t have tube seeing, but the front ERF closes off the tube, so it is no longer an open system and there might be temperature gradients that cause thermal air currents.

Has anybody using a C8 (or C9.25/C11/C14) for solar imaging observed something similar? And maybe taken measures to control/minimize tube seeing? (Somewhere I have seen C8s wrapped in aluminium coated bubble foil to prevent tubus seeing at nighttime. Might that be useful for solar imaging purposes, too?)

Regards,

Frank


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Re: CaK – 30th July

Post by marktownley »

These are excellent Frank! I have found similar thing with my 100mm Tal, i'm using rear mounted ERF (on the CaK module) - had had similar thoughts as you. With my 8" HaT I installed Tempest Cooling fans https://www.deepspaceproducts.com/temp- ... _9331.html which seem positive. My issues with the larger scope is the atmospheric seeing rather than tube currents.


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Re: CaK – 30th July

Post by Montana »

These are absolutely superb!!! I do love a good CaK :hamster: :bow :bow

One thing that is noticeable (only because I like to look super up close) is that the top left hand side is much more in focus than the bottom right, any thoughts?

Alexandra


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Re: CaK – 30th July

Post by LTHB »

Thanks, Mark&Alexandra!

Alexandra, the Mewlon is an uncorrected Dall Kirkham, so tack-sharp on axis, but showing coma off-axis. Even on the rather small sensor of the ASI174 you see it if you are looking closely in the corners, as you did. The asymmetry (top left vs. bottom right) is the result of my cropping the picture asymmetrically: The image was the first of my afternoon session, I had just set up the scope, not yet picked a target area to image, and started focusing, when I noticed the jaw-dropping seeing. So I hastily finished focusing and hit the "start" button without bothering to pick a particular patch of the solar surface or even to center the wing-like plage structure I had used for focusing that had drifted to the lower right corner. Which proved to have been the right thing to do: The seeing, while still okay for a while afterwards, never got that good again, so I used the image as I had it, and, as usual, cropped it to remove most of the coma affected margin, but cropped it asymmetrically to have the plage structure at least near the center.

So next time I start setting up five minutes earlier... Image

Regards,

Frank


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Re: CaK – 30th July

Post by MapleRidge »

Hi Frank...

The CaK images are excellent :bow

The coma you describe is unfortunate since the scope does produce a very nice CaK image where the aberration is minimized.

Brian


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Re: CaK – 30th July

Post by christian viladrich »

Hello Franck,
You might try to install a thermal probe next to the mirror. You could then check whether this is an issue with tube turbulence.
Best regards
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Re: CaK – 30th July

Post by Carbon60 »

The sharpest parts of the images really are very good, Frank.

Stu.


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Re: CaK – 30th July

Post by MAURITS »

Very nice captures Frank.


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Re: CaK – 30th July

Post by LTHB »

Thanks, Brian, Stu and Maurits!

Christian, a thermal probe is an interesting idea, but the Mewlon does not have any openings for a cable to pass through. My idea was to use a thermal imaging camera that can measure surface temperatures; I may have access to one, so probably I will try that in the next weeks.

Regards,

Frank


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