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

[christian viladrich]

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.


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 :-)


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 :

Clear skies !
Christian

[marktownley]

Crazily excellent images Christian! You need a bigger scope

[eroel]

Christian:
Superb shots.
Best regards,
Eric.

[ffellah]

The resolution is incredible, Christian !

Franco

[bart1805]

Dream like images, just spectacular!

[christian viladrich]

Thanks to all :-)
Here is an image of the observing site :

[krakatoa1883]

For my location 0.3 arcsecs are science fiction

15 frames only for each of the images?

[pedro]

Outstanding images Christian. I agree with Mar, you need a bigger telescope

Where did you get the G band filter?

[christian viladrich]

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.

[MalVeauX]

Super resolution, always a pleasure!

Very best,

[Carbon60]

Absolutely remarkable images, Christian.

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

Stu.

[christian viladrich]

Thanks Marty and Stu :-)
It's easier to get up there with a 4WD. There is no cable car.

[Derek Klepp]

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

[Montana]

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

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

Alexandra

[bart1805]

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.

[christian viladrich]

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).

[bart1805]

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.

[christian viladrich]

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.

[bart1805]

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. (-;