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Possibly one of the last active regions of cycle 24? AR12757 ends january with decent activity for solar minimum. Taken by Marty Wise with his 8" SCT, Aries ERF and PST mod.

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Moving forward from solar cycle 24 to 25

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by christian viladrich
Tue Jan 21, 2020 8:40 pm
Forum: Solar Reference Library
Topic: HR solar spectra
Replies: 3
Views: 142

HR solar spectra

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....
by christian viladrich
Sun Jan 12, 2020 10:04 am
Forum: Solar Scope Modifications
Topic: How close to F10 must a PST mod truly be?
Replies: 14
Views: 290

Re: How close to F10 must a PST mod truly be?

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.
by christian viladrich
Sun Jan 12, 2020 9:59 am
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Blocking filters and wintertime
Replies: 20
Views: 979

Re: Blocking filters and wintertime

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...
by christian viladrich
Sun Jan 12, 2020 9:47 am
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Why no DSLR cameras?
Replies: 8
Views: 348

Re: Why no DSLR cameras?

In the old time, we were using BW films, for example Kodak Microfile AHU, Kodak TP 2415, etc.
by christian viladrich
Mon Jan 06, 2020 7:40 pm
Forum: This is SolarChat !!
Topic: AR2736 in Ca K on 24 March 2019
Replies: 7
Views: 127

Re: AR2736 in Ca K on 24 March 2019

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. ...
by christian viladrich
Sun Jan 05, 2020 5:44 pm
Forum: This is SolarChat !!
Topic: AR2736 in Ca K on 24 March 2019
Replies: 7
Views: 127

AR2736 in Ca K on 24 March 2019

Dear All,
Here is an old image which has been on my HD for many months. Not much activity at that time ...
Image
Best wishes for the new year !
by christian viladrich
Fri Dec 20, 2019 11:00 am
Forum: Solar Scope Modifications
Topic: Motorized Etalon Tuners
Replies: 13
Views: 528

Re: Motorized Etalon Tuners

Well done !!
by christian viladrich
Fri Dec 20, 2019 10:59 am
Forum: Solar Scope Modifications
Topic: 12" White light Newtonian
Replies: 7
Views: 532

Re: 12" White light Newtonian

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...
by christian viladrich
Fri Dec 20, 2019 10:49 am
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Why no DSLR cameras?
Replies: 8
Views: 348

Re: Why no DSLR cameras?

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.
by christian viladrich
Wed Nov 13, 2019 8:08 pm
Forum: This is SolarChat !!
Topic: Mercury Transit
Replies: 11
Views: 284

Re: Mercury Transit

Well done !
by christian viladrich
Wed Nov 13, 2019 8:07 pm
Forum: This is SolarChat !!
Topic: Mercury transit and proms
Replies: 16
Views: 371

Re: Mercury transit and proms

Excellent indeed, congratulations !
by christian viladrich
Wed Nov 13, 2019 8:06 pm
Forum: This is SolarChat !!
Topic: Mercury Solar transit 11th of November 2019.
Replies: 13
Views: 311

Re: Mercury Solar transit 11th of November 2019.

Beautifull images Eric, well done !
by christian viladrich
Tue Nov 12, 2019 7:58 pm
Forum: This is SolarChat !!
Topic: Autostakkert2 flats issue
Replies: 8
Views: 266

Re: Autostakkert2 flats issue

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.
by christian viladrich
Sat Nov 09, 2019 7:16 pm
Forum: Solar Scope Modifications
Topic: PST mod on a C14
Replies: 11
Views: 941

Re: PST mod on a C14

It would also need large pixel size and / or a focal reducer after the etalon. Otherwise, the image scale would be way too large.
by christian viladrich
Fri Nov 08, 2019 1:39 pm
Forum: Solar Scope Modifications
Topic: PST mod on a C14
Replies: 11
Views: 941

Re: PST mod on a C14

Here is the sweet spot radius depending on the max CWL allowed and on the focal length of the telescope:
Image
by christian viladrich
Fri Nov 08, 2019 1:13 pm
Forum: Solar Scope Modifications
Topic: PST mod on a C14
Replies: 11
Views: 941

Re: PST mod on a C14

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...
by christian viladrich
Mon Oct 14, 2019 9:19 pm
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Strehl ratio for a Celestron C11
Replies: 7
Views: 505

Re: Strehl ratio for a Celestron C11

What aperture did you use to take this image ?
by christian viladrich
Mon Oct 14, 2019 6:36 pm
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Strehl ratio for a Celestron C11
Replies: 7
Views: 505

Re: Strehl ratio for a Celestron C11

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/...
by christian viladrich
Tue Sep 17, 2019 8:14 am
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: What do you think is the most versatile high resolution solar telescope design?
Replies: 43
Views: 3341

Re: What do you think is the most versatile high resolution solar telescope design?

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...
by christian viladrich
Mon Sep 16, 2019 4:43 pm
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: What do you think is the most versatile high resolution solar telescope design?
Replies: 43
Views: 3341

Re: What do you think is the most versatile high resolution solar telescope design?

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_...
by christian viladrich
Sun Sep 15, 2019 2:12 pm
Forum: This is SolarChat !!
Topic: H-alpha 31 august, 7 inch Intes, reflections and a BF30.
Replies: 15
Views: 810

Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Hello Bart,
This is a quite good image. Getting rid of these reflections is quite tricky. Keep us posted !
Christian
by christian viladrich
Sun Sep 15, 2019 11:54 am
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: What do you think is the most versatile high resolution solar telescope design?
Replies: 43
Views: 3341

Re: What do you think is the most versatile high resolution solar telescope design?

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...
by christian viladrich
Sun Sep 15, 2019 11:24 am
Forum: Solar Scope Modifications
Topic: A big solar newton for ultra narrowband imaging, possible?
Replies: 30
Views: 1618

Re: A big solar newton for ultra narrowband imaging, possible?

I also have the TS concenter. It is indeed quite good to align the secondary mirror of the 300 mm solar Newtonian.
by christian viladrich
Sun Sep 15, 2019 11:23 am
Forum: Solar Scope Modifications
Topic: A big solar newton for ultra narrowband imaging, possible?
Replies: 30
Views: 1618

Re: A big solar newton for ultra narrowband imaging, possible?

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...