HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

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christian viladrich
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HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by christian viladrich » Sat Sep 01, 2018 7:53 pm

Dear All,

Here are some more images taken from 2930 m high at St Véran site with the 300 mm solar telescope. The seeing conditions oscillated continuously from very bad to excellent.
The first image was taken in G band (430 nm FWHM 1.9 nm). The resolution is limited by the 300 mm aperture of the scope. There are many filigrees in the intergranular region embeded in the group of pores.
Image

The second image was taken in K-line (which is not Ca K ..) at 396 nm FWHM 10 nm. This is my very first diffraction limited image taken with the 300 mm in this wavelength :-)
Image

The resolution is a tad higher compared to 430 nm. The filigrees are also visible, with some more contrast.

Meanwhile, the area of AR2720, also taken at 396 nm, was crowded with filigrees :
Image
Clear skies !
Christian
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by marktownley » Sat Sep 01, 2018 10:43 pm

Crazily excellent images Christian! You need a bigger scope ;)
Image
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by eroel » Sat Sep 01, 2018 11:39 pm

Christian:
Superb shots.
Best regards,
Eric.

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by ffellah » Sun Sep 02, 2018 12:16 am

The resolution is incredible, Christian !

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by bart1805 » Sun Sep 02, 2018 6:50 am

Dream like images, just spectacular!

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by christian viladrich » Sun Sep 02, 2018 8:52 am

Thanks to all :-)
Here is an image of the observing site :
Image
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by krakatoa1883 » Sun Sep 02, 2018 11:32 am

For my location 0.3 arcsecs are science fiction :lol:

15 frames only for each of the images?
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by christian viladrich » Sun Sep 02, 2018 1:19 pm

Thanks Raf and Pedro !
Raf : yes, there are only 15 frames in each stack. The IMX174 is an amazing sensor.
Pedro : this is a filter from Andover. It is listed in the "surplus". Indeed, I think that a 400 mm would be appropriate to the conditions up there.
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by MalVeauX » Sun Sep 02, 2018 2:47 pm

Super resolution, always a pleasure! :bow

Very best,

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by Carbon60 » Sun Sep 02, 2018 7:57 pm

Absolutely remarkable images, Christian.

Do you drive to the site, or is it accessible only by cable car?

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by christian viladrich » Sun Sep 02, 2018 8:29 pm

Thanks Marty and Stu :-)
It's easier to get up there with a 4WD. There is no cable car.
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by Derek Klepp » Mon Sep 03, 2018 6:27 am

Great pics and great site.Nothing that high here in Australia.

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by Montana » Mon Sep 03, 2018 9:26 am

Wow!!!!!!! mouth watering and I am dribbling :lol:

Last night I booked a holiday only 20km from Pic du Midi :hamster: I wonder what will be filling the car with on that holiday :)

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by bart1805 » Mon Sep 03, 2018 10:23 pm

Hi Christian, like Raf each time I see your pictures it is a surprise that you stack such a small amount of frames. It is quite the opposite compared to my own workflow, but your pictures inspired me to go through some old data and use far less frames than I usually do. And I am surprised. I can use less LR deconvolution and about the same or a bit more unsharp masking to create better results when using these numbers of frames:
15 - 20 frames in white light / Solar continuum
30 - 50 frames in Cak
45 to 70 frames in H-alpha.
Thanks again for the beautiful pictures and for the inspiration. CS! Bart.

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by christian viladrich » Tue Sep 04, 2018 7:22 pm

Thanks Derek, Alexandra and Bart :-)

Alexandra, it is possible to spend a night at the Pic du Midi observatory and have access to a 50 cm Dobsonian telescope. You have to book in advance.

Bart, you have a keen eye ;-)
The number of images you have to stack depends on the S/N of each image, which depends on :
- the full well capacity of the sensor (= max number of electrons by pixel), the higher the better. The IMX174 is excellent in this respect.
- the seeing : better seeing means better S/N.

Then, if the quality of the stacked image is better, its contrast is higher, meaning the processing can be less agressive.

Typically, I have :
- 7 to 30 frames in WL (gain of the camera set to the minimum),
- 30 to 60 frames in Ca K ,
- 200 to 300 images in Ha (gain of the camera set to high).
Christian Viladrich
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by bart1805 » Tue Sep 04, 2018 7:55 pm

Thanks Christian. I try to image H-alpha with low gain, so maybe that is the reason I could use fewer frames. But will try it with high gain and more frames to stack: shorter exposure time so better freezing of the seeing.
Gamma is always neutral when you image in these three wavelengths?
CS! Bart.

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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by christian viladrich » Wed Sep 05, 2018 6:31 pm

Bart,
I dont' remember the sensor you have. If you have a CMOS sensor with low read noise (IMX174, IMX290, etc), then the following apply to set the gain when the level of ligh is low (i.e. Ha imaging) :
1) Set the exposure time to the value giving the max fps of the camera (e.g. if the max fps is 150 fps, then you set the exposure time to 6.6 ms).
If the camera max fps is low, then set the exposure time to about 6 - 8 ms (the shorter the better).
2) Set the gain in order to have the max value of the histogram to about 70to 80%.
This is all :-)

I use gamma = 1 for all types of images except prominences. It is better to tune the gamma during processing rather than during acquisition.
Christian Viladrich
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Re: HR images taken at 396 and 430 nm on August 24 with the 300 mm solar scope

Post by bart1805 » Wed Sep 05, 2018 8:19 pm

Thanks Christian!
I use the Grasshopper version with the IMX174 sensor. So for one thing, I can't blame the camera if I compare my images with yours. (-;

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