My 10 cents : With a 8-inch SC : - with the appropriated filter : photosphere is OK from about 450 nm and beyond, - with the appropriated filter : chromosphere is OK in Ha. In a nutshel, a C8 (EdheHD or not) is useless for K-line ou Ca K imaging because it is not diffraction limited below about 450 ...

Hello Raf, Your image with the TMB80 F/11.7 is quite good and is representative of the resolution that can actuallly be reached with a 80 mm in Ca K. On my side, I had found that the (old) Taka FSQ 106 was good when stopped down to 80 mm. The new Taka FSQ seems to have an improved blue correction. T...

You nailed it Peter. This is a wonderful analysis. Many thanks !
So it takes something like 0.3 to 0.5 A FWHM to show the filaments in Ca K (depending on the expected contrast).

I think Mark W told once that narrow band Ca K etalons are more difficult to do than Ha etalons ? I am not 100% sure.

It looks like that the filaments are best visible in the range of plus / minus 0.080 A.
This means that a filter should have a FWHM < 0.16 A to show any filaments.

Hi Peter,
This is great !!
Could you display the individual frames in a single large image, just like you did for Ha ?

To Mark and Bob,
The K-line is a marvellous filter to block any leakage outside a 10 nm band arround 396 nm, from 300 nm to 1700 nm.
So the issue should be related to the CWL.
F/25 and some tilt might set the case.

To Bart : - Yes, the Hershel wedge is used without any density filter. - Regarding Baader Planetarium policy, my guess - and this is just a guess - is that they don't want to take any risks. It is impossible for them to know whom they are selling the filters to. Beginners or experienced amateurs loo...

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 1...

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 dep...

Ok ... I didn't want to jump into this, but it seems there is some misunderstanding about filter transmision and exposure time ;-) Let's start with the exposure time required for high resolution imaging and a K-Line filter (396 nm, about 8 nm FWHM): 1) With an Hershel diagonal, the exposure time is ...

Bob, you should probably have to jump to F/20 for the next tests. F/9 is definetly to short for a 1 A filter.

Interesting tests Bob ! It looks as if the filter is out of band, while it is supposed to be at 393.37 nm with no drift with temperature ? The resolution is definitly lower compared to the Coronado CaK, but it might just be an artefact of variable seeing conditions. Diffuse light and reflections is ...

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

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.

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

Nice granulation Pedro !
Did you use any filter ?

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 sco...

Thanks Stu and Franco :-)

Alexandra, here is the website of Astroqueyras :
https://www.astroqueyras.com/

It is easier to get up there with a 4-wheel drive.

Thanks !
Marty, my guess is that a 250 mm aperture is the minimum. But it would be worth to try it with a 200 mm aperture.

Hello Frank, If I have a suggestion, this would be to forget about deconvolution and only apply an unsharp mask. Deconvolution won't replace a lack of resolution in the image. Here is a recent Ca K image taken with the TOA 150 : http://astrosurf.com/viladrich/astro/soleil/wl/2018/CaK-4August2018-9h3...

Hello Eric,
Very nice FD and proms !
Christian

Dear All, Here are some first images taken at the site of St Véran observatory (2930 m) with the 300 mm solar telescope. I use a 430 nm FWHM 1.9 nm filter. A small pore with another small one on the left side of the image. Many filigrees are visible in the intergranular region : http://astrosurf.com...

Marvellous and very informative. Thanks for sharing !
Could you slow do a little bit the movie ?
It seems to me that the "spicules bushes" are best visible at +/- 0.4A.
Could you make another monatge with larger resolution ? Let's say with the solar disk twice the size of this first montage ?

Beautilful resolution !
I was thinking you might give a try with an OIII filter.

Hello Alessandro,
A lot of resolution there ! And very nice processing too.