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-...

Hi, Now, here are the images taken in Ha with the C8 under excellent seeing condition at F/35 : http://www.astrosurf.com/viladrich/astro/soleil/wl/2019/Ha-18August2019-7h44minUT-C8-B1920-PE06A-N35.jpg http://www.astrosurf.com/viladrich/astro/soleil/wl/2019/Ha-18August2019-8h22minUT-C8-B1920-PE06A-N3...

No, I have not tested nor calculated it. If I take the example of a SolarSpectrum or DayStar etalons, there is already a 5 to 10 A BF in the body of the filter Adding a 4 A BF gives a little bit more contrast (see my test pages). The real benefit is with the addition of a 1.5A filter. I also tested ...

Thanks !
Alexandra, I am contacting a friend who is a specialist of solar physics. I hope to have more information.

Hi Mark, The question of tilt / collimated or telescentric beam starts to become an issue with filters narrower than about 2 to 3 A. BF are usually about 5 to 10 A. So, it should not be a big issue. Regarding stacking an etalon and a BF, I've done many tests. For example here with a top quality 1.5 ...

Thanks guys !
Stu, I'll try and get the information.
Mark, this is my 300 mm solar Newton :
http://www.astrosurf.com/viladrich/astr ... /N300.html

Dear All, Here are some more images taken at St Véran with the 300 mm Newtonian. August 15th, with the 396-5 nm filter. There is an incredible variety in the granulation cells. Some are very dark. In some parts, the intergranular region is very dark too : http://www.astrosurf.com/viladrich/astro/sol...

The Internet is back at St Véran ...
Thanks Bart, Stu and Mark !

Thanks to all !
Today was no good. We hope to-morow will be better.
Best wishes

Dear All, Nice seeing condition this morning at St Véran (2930 mm) with the Newton 300 mm. This image was taken with an Andover 396 - 5 nm which appears to give excellent results. More to come in the next days. http://www.astrosurf.com/viladrich/astro/soleil/wl/2019/13August2019-8h16minUT-N300-396-5...