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.
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).
Mg II in UltraViolet
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Re: Mg II in UltraViolet
Christian Viladrich
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Re: Mg II in UltraViolet
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.
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.
Raf
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Re: Mg II in UltraViolet
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.
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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Re: Mg II in UltraViolet
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
Hmmm
Once we have solved all these technical difficulties....
What about a camera which can record that far into the UV??????
Once we have solved all these technical difficulties....
What about a camera which can record that far into the UV??????
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Re: Mg II in UltraViolet
" Here are the simulations for a re-spaced classic C8 :
http://astrosurf.com/viladrich/astro/in ... -Plate.htm "
Thanks so much for this Christian!
http://astrosurf.com/viladrich/astro/in ... -Plate.htm "
Thanks so much for this Christian!
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