Just for information, another source for HR solar spectra, Paris Observatory : https://lesia.obspm.fr/perso/jean-marie-malherbe/posters/poster1.png https://lesia.obspm.fr/perso/jean-marie-malherbe/posters/poster2.png https://lesia.obspm.fr/perso/jean-marie-malherbe/posters/poster3.png https://lesia....

Ken said it all :-)
It does not matter whether you have to add some Barlow lens (or equivalent) to reach F/10. The important thing is to have an incoming F/10 beam at the entrance of the PST collimating lens.

As an additional info, the CWL drift with temperature also depends on the substrate (e.g. BK7 versus fused silica) and on the technology (soft coating versus hard coating). Hard coating and BK 7 have a lower drift with temperature. For example, 0.004 nm/°C for fused silica and hardcoating in near UV...

In the old time, we were using BW films, for example Kodak Microfile AHU, Kodak TP 2415, etc.

Thanks to all :-) JochenM, I used a Takahashi TOA 150 refractor with an ASI290 camera and a Barr Ca K filter. There is a 50 mm blue Astronomik filter placed in internal position as a sub-aperture ERF. There is also a 393-10 nm Edmund Optics filter providing additional protection to the Ca K filter. ...

Dear All,
Here is an old image which has been on my HD for many months. Not much activity at that time ...

Best wishes for the new year !

Well done !!

As said by Alexandre, just keep the primary uncoated and the secondary coated. Regarding filters, it all depends on the seeing conditions at your place. A 300 mm is a bit of a large telescope for solar image. The range of usual filters are : - deep-sky Ha, when seeing is bad, - 540 nm, when seeing i...

To expand a litlle bit futher on what Rainer said, with a DSLR camera we only have one pixel out of four which is sensitive to Halpha.
This means that resolution is divided by about 2 compared to a black and white sensor.

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...