Mg II in UltraViolet

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christian viladrich
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Re: Mg II in UltraViolet

Post by christian viladrich » Sun Nov 11, 2018 7:16 pm

Hello Bob,

Here are the simulations for a re-spaced classic C8 :
http://astrosurf.com/viladrich/astro/in ... -Plate.htm

The diffraction limited flat-field increases by a factor of four when the Schmidt plate position is set 230mm ahead its nominal position.
Image

There is no impact on the spherochromatism (= still very bad in near UV).

As for the correction in near UV light, there are several issues :
- the spherical aberration changes rapidely with wavelength below 420 mm. This is why the Strelh ratio drops drastically below 420 mm ;
- in order to design a spherical aberration corrector, we would need to know with good accuracy what is the actual shape of the Schmidt plate ;
- this is why ASH actually measured the Schmidt plate of a C8 to design a Barlow lens for this specific C8.

My guess is that a 200 mm F/8 Newtonian telescope is much more appropriated to high resolution Ca K imaging.

I hope to run some tests in Ha on my 300 mm Newtonian with a sub-aperture ERF. If things go well, the next step will be to make a small aperture Ca K ERF filter.

I still have the option open for a ERM coating on my 300 mm scope. The idea would be to have a coating reflecting red (for Ha) and near UV light (for Ca K).
Christian Viladrich
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krakatoa1883
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Re: Mg II in UltraViolet

Post by krakatoa1883 » Sun Nov 11, 2018 8:04 pm

In my opinion for hires imaging in the near UV correcting the system for SA is much more important that enlarging the D-L field, thus an all-reflecting system would definitely be much more preferable than modifying a SCT.

BTW, one can consider a commercial Cassegrain, it is a relatively inexpensive scope that can be modified to make it better suited for solar work.
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christian viladrich
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Re: Mg II in UltraViolet

Post by christian viladrich » Sun Nov 11, 2018 8:31 pm

Interesting info Raf :-)
I didn't know they have these small size Cassegrain scopes.They have quartz mirrors which is very nice. I have no idea of the optical quality.
Christian Viladrich
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george9
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Re: Mg II in UltraViolet

Post by george9 » Sun Nov 11, 2018 8:56 pm

They also have a 12" classic Cassegrain from Orion Optics UK, although it costs four times as much. 25% obstruction (vs 33% on the smaller ones). Comes with a Ronchi test, but no mention of minimum performance. George

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Re: Mg II in UltraViolet

Post by Merlin66 » Sun Nov 11, 2018 11:07 pm

Hmmm
Once we have solved all these technical difficulties....
What about a camera which can record that far into the UV??????
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eroel
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Re: Mg II in UltraViolet

Post by eroel » Mon Nov 12, 2018 12:57 am

Valery:
A good thread with super shots and info.
Best wishes,
Eric.

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Bob Yoesle
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Re: Mg II in UltraViolet

Post by Bob Yoesle » Mon Nov 12, 2018 12:48 pm

" Here are the simulations for a re-spaced classic C8 :
http://astrosurf.com/viladrich/astro/in ... -Plate.htm "

Thanks so much for this Christian!
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