Thoughts on a further modified PST:

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I need another helical focuser after the TS one fell in half. A conventional focuser won't work because the focusing has to be at the end of the long, PST filter extension. The etalon has to be in the correct position, relative to the focus of the telescope objective. [200mm inside focus.] Then the rest of the PST filters have to be in the correct place relative to the eyepiece to avoid vignetting as the eyepiece reaches focus.

Sunday's proms 080919.

In the unmodified PST the simple, 1.25" eyepiece socket [holder] is part of the ITF and Blocking filter assembly. Focusing is via moving the prism. Which is removed for heavily modified PST, H-alpha systems like mine.

It might be possible to build a framework for the entire etalon/filter chain. Then a normal reflector focuser could sit on a plate on the end to carry a compact focuser in the correct place. I have a cheap 2" Crayford, reflector focuser which fits on a short SCT tubular adapter. This was fitted to a round plate for my 5" home made refractor. Ready made for the job.

I have wanted to have adjusting rods for the internal, Baader D-ERF. This could be tied into the new mods rather than drilling the existing OTA back plate for longer rods. A cooling fan has also seemed worth trying. Probably drawing air downwards from slots or holes around the rear of the objective end of the tube and past the 90mm internal filter. Though this is presently built onto a solid baffle. Which prevents any air movement. A ring of holes could easily be made to allow forced air flow.

The [live] active area of the SharpCap screen, when set to 640x960. Showing the Solar limb with prominences on my 27" AOC monitor. ZWO 120MC USB3 camera with 2x WO Barlow on its nose. 150/8 [120 F/10 equivalent] with internal D-ERF + PST H-alpha etalon and filtration.

If I could get a 6" f/10 objective and full aperture D-ERF I could start from scratch with a whole, new, H-alpha OTA. But think of the cost buying all new components! A fraction of the cost of a commercial, 150mm, solar telescope but still a heavy outlay.

Then there's the option of a Daystar Quark filter instead of the modified PST. I could still use the 6" f/8 with a Quark. All this during a possibly deep, Solar Minimum? Is it really worth it? Are proms alone worth the very considerable investment? Quarks seem to be highly variable in image quality and even in reliability. With tales of returns and fourth and fifth replacements! Making the £1500 investment quite a gamble. Will some completely new, solar filtration system come onto the market? Perhaps thanks to commercial pressures to lower costs during a Solar Minimum? The trend is towards larger apertures, SCTs with full aperture filters. The results can be stunning but at what cost?

Click on any image for an enlargement.

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