Well done !

Excellent indeed, congratulations !

Beautifull images Eric, well done !

The flat image is to be calculated by AS.
So, first record the flat as an AVI (or SER) file.
Then process this AVI or SER file in AS to calculate the flat image (PNG or TIF).
Then use this flat image in AS.

It would also need large pixel size and / or a focal reducer after the etalon. Otherwise, the image scale would be way too large.

Here is the sweet spot radius depending on the max CWL allowed and on the focal length of the telescope:

Indeed,in a telecentric system: - F/30 and above is "good" with mica-spaced etalons: http://astrosurf.com/viladrich/astro/instrument/solar/FWHM-N.JPG - F/50 and above is needed for air-spaced etalons : http://astrosurf.com/viladrich/astro/instrument/solar/Fig7.82-air-spaced-etalon-FWHM-FD.jpg In a c...

What aperture did you use to take this image ?

Here are some actual interferometric measurements (HASO) of the Strelh ratio of various C11 OTA (EdgeHD or not) at 473 nm : https://www.airylab.com/contenu/mesures/astro/rapport%202015-35003-a.pdf https://www.airylab.com/contenu/mesures/astro/rapport%202012-33001.pdf https://www.airylab.com/contenu/...

Hello Valery, Going back to the initial question of this post, and after the tests recently done à St Véran, I agree that the combination of a large ERF and a reflecting telescope is the best HR solar telescope in large diameter. The Cassegrain configuration is indeed very attractive. Best regards C...

Hi, I would like to go back to the question of spherochromatism which is inherent to the Schmidt- Cassegrain design. As I have already said, this is nothing new, optics beeing optics. Let's see what Celestron wrote in their White Paper : https://s3.amazonaws.com/celestron-site-support-files/support_...

Hello Bart,
This is a quite good image. Getting rid of these reflections is quite tricky. Keep us posted !
Christian

Yes, indeed !
Thanks Bart

Hello langleif2, Spherochromatism in Schmidt-Cassegrain is nothing new. You can open any good books on telescope optics to get some information on it. This is just basic optics. You can read for example the two books I co-authored with some friends (unfortunately in French language for now) ;-) Ther...

I also have the TS concenter. It is indeed quite good to align the secondary mirror of the 300 mm solar Newtonian.

Hello langleif2, This is a textbook example of loss of information in a communication process : A tells a story to B, which B repeats it to C, etc. After a short while the story becomes quite another story :-) So here the actual story : Every year, we have a solar gathering at Serbannes (France). Ne...

430 nm filters are available at Edmund Optics with 10, 25 and 50 nm FWHM, and also at Andover Optics (2 nm FWHM).

Hello lanleif2, thanks for this clarification. I am afraid you were a bit mislead. I know rather well AiryLab and MCM. Alex do so since he is the one you got his 250 mm coated by MCM. So far, this is the larger Newtonian telescope with such a coating on the mirror. This telescope and MCM coating is ...

The DOT is a Gregorian telescope, not a Netwonian. This is a huge difference and explains why a cooled diaphragm can be installed at the primary focus. Remember that in a Gregorian telescope the focus of the primary mirror is in front of the secondary mirror, not behind. This makes thing much easier...

We were on top of a mountain, 2930 m altitude. Ambient temperature was from 2°C to about 15°C.
So an increase of 10°C is huge. Basically, a delta of more than 2°C between ambient air and an optical part is detrimental to the seeing.

Unfortunately, these tests proved that this idea was a dead end. For Ca K imaging with my TOA150, the 50 mm internal ERF is 33% of the diameter of the objective. I have no internal turbulence. With the 300 m Newtonian of Alex, the ratio is 16%. Now, we can say this is too low... Maybe, another facto...

Hello STu,
Thanks a lot for your input.
Could you tell us a little bit about the differences between iron perchloride et HCl ? I understood than the first one is less agressive ?

Thanks to all :-)
I like the fourth one too !

Well done Alfred !

The Internet is back at St Véran .. Here is a set of pictures taken on August 21 with the 300 mm Newtonian and the 396-5 nm filter. Let's start with a region close to the Eastern limb, with many faculae and darker areas. http://www.astrosurf.com/viladrich/astro/soleil/wl/2019/21August2019-8h03minUT-...