SolarChat!

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).

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.

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.

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

Hmmm
Once we have solved all these technical difficulties....
What about a camera which can record that far into the UV??????

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

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

Thanks so much for this Christian!