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The Corona again - finally!

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#1 Klaus_160


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Posted 07 May 2021 - 05:05 PM

It's been a long long long long time since I have last observed the Corona. Work commitments, weather, and, ironically enough, Corona (restrictions) have prevented me from going out to mount Mitchell since last November. (https://www.cloudyni...rona-yesterday/)


However, yesterday was the day, finally!


Now since then, I have made some equipment improvements:


I have now made a full set of cones for the 2" instrument (before I only had one cone, the “Corona cone” which is the second one from the left in the picture).


20210104 204925


The instrument is now riding on a dual motorized advanced Polaris mount. This is much more convenient than the single axis drive of the new Polaris, and the bubble level/compass you can add to align the mount is really helpful during daytime observations.


20210506 102452


So anyway, I set out early in the morning since the weather forecast was okay enough and there was an active region starting to rotate onto the disk.


euvi 195 heliographic



I arrived at 8:20 AM and set up my equipment. The sky was only so-so and I was doubting whether I would be able to see anything. I scanned the limp with the filter, first using the achromatic objective which had still left in from the setup trial the day before. However I really couldn't see anything.


Then, I switched to the singlet repeated the procedure. Initially I did not see anything, but then I checked the orientation and where I would expect the region to show, and after two minutes of fiddling I was actually able to see a brightening at the expected spot. I just focus, and good moments I could see a few faint rays coming from the limp. These structures were really weak though, and the observation, while certain, was pretty marginal. This maybe the weakest I had seen the Corona, except maybe for second time in November.


However, just to try, I switch back to the achromat and I was actually able to still see the region, somewhat to my surprise. It wasn't quite as clear as with the singlet, but it was there and still readily apparent. I guess if the sky is not that great, that levels the playing field between the single lens in the achromat against.


I switched back to the singlet and then I took out the cameras in order to produce some pictures as a record. I started with my trusty old IMX249. This is the original camera, but the chip is not large enough to produce a one-shot image. 


raw full frame image
imx249 level
adjusted full frame image
imx249 crop
cropped region
imx249 level crop


cropped region level adjusted



The region is clearly visible, but really weak. However, as you can see, right in that region there is a speck of dust on the camera which I did not realize while taking the images. Oh well.


Then I switched over to my newly acquired IMX253 which has a chip size of 1.1 inch and therefore can fit the whole field of view into one-shot.


Again, RAW full frame
imx253 level
Level adjusted full frame
imx253 crop
The region cropped
imx253 level crop

The region cropped and level adjusted



Please note that the orientation is different between the cameras because I just put the camera into the focus of the random orientation. I didn't pay attention at the time.


Also, you will note the graininess of the image which is the result of the high gain that I had to use. Smaller pixels because less like a pixel equals higher exposure time at the same f-number.



Now for comparison, here is the SDO 171A image from the date and time of my observation


171A full
Flipped (because I used a diagonal) and rotated
171A full Rot
And cropped to the region
171 A crop


Now I have discovered a new feature in PowerPoint: making images transparent! So here is a series of overlays of the imx253 and the SDO with changing transparency. I think this is pretty neat!


171 A crop
171 A crop  6
171 A crop  5
171 A crop  4
171 A crop  3
171 A crop  2
171 A crop  1

Overall, I was pretty pleased with my outing. For one, it has been a really long time since I have seen the Corona was good to be able to repeat it in any case. Secondly, I determined that an achromat can also work which I find quite interesting and did not expect. And then a confirmed that my new setup works well, which includes the mount, the cones and the camera.


The next big step would be to finally get the correct filter for 5303 Å instead of the tilted 5320 Å filter combination I have to use. What I have now is too wide and scanning the limb gets old - and it also ruins the appearance especially if you have ARs on the opposite sides. I am trying to acquire one through solar spectrum, but that process has been slow. :(

Edited by Klaus_160, 08 May 2021 - 11:44 AM.

  • BYoesle, George9, HPaleske and 11 others like this

#2 BinoGuy


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Posted 07 May 2021 - 05:12 PM

Wow, extremely comprehensive review Klaus_160.  Such great images!   Thank you for sharing.



Clear Skies  BG  º¿º

#3 jwestervelt


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Posted 07 May 2021 - 06:31 PM

Wow.  Very nice.

#4 George9


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Posted 08 May 2021 - 07:12 AM

Awesome match, and continued amazing progress.


(I continue to work on mine, but without a 530.3nm filter, I can just watch the dim proms in H-alpha.)



#5 ch-viladrich


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Posted 08 May 2021 - 12:52 PM

Marvellous again !

I hope you can get hold of a nice green line filter pretty soon.

Keep us posted.


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