90mm TS Triplet Mod

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AndiesHandyHandies
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90mm TS Triplet Mod

Post by AndiesHandyHandies »

Hi

1. Stage 1 PST Mod.

Used the same set up as on the 127mm with 2x ED Barlow un-screwed nosepiece before the Etalon, AOK Swiss T2 low profile adapter and T2 to 48mm.
And a Baader 2" UV-IR on 4 2" Extension tubes in front. With 48-43mm step down ring as a baffle for the front of the focusser tube on the 127mm.

The main problem is reflections of the sides of the pentaprism washing the field despite 2 stops in the black box, entrance and exit. And flocking inside for transmissions through the un-silvered prism sides.
One advantage of the Vixen is the secondary shades direct light from entering the etalon. So the prism reflections are less bright despite the greater aperture.
Also the 127mm is better baffled it looks like. Larger tube and more baffles.

Works but dimmer image than the 127mm.

2. Stage 2 PST Mod

Replaced the black box with a diagonal with a 1.5A Cosmetic Seconds Omega Bobs filter mounted in it with a tilter, as the Comb filter. Thanks to RodAstro. One of his double set for H-alpha.

Of course forgot to take the re-focussing lens out the back. Though makes little difference.
It has the Omega 40nm blocker from my H-alpha set in the front in place of the Collimating lens. 'Combat'.

Seem to have an extra reflection, off the back of the etalon?

The Bobs filter has a slight internal reflection on one side. So I rotated the set so the two reflections were together.

The Sun exactly filled the field of the 25mm Plossl so the barlow is working at 4x as RodAstro measured on the stars.
The extension tube set had to come out a few 10s of mm to reach focus. Less backfocus than 127mm.
So working at F26.8 straight through.

Set Bobs filter at maximum tilt and brought back till on band. Keep various reflections and artefacts out of the field.
I also put one of my 'Moon filter' stops in the front of the diagonal and one in the T2 1.25" eyepiece holder screwed onto a 2" T2 front to go into the back of the diagonal, to reach 200mm back focus on the PST black box. That reduced the artefacts in the field.

So had a view of spiricules and prominences against a darkish background.

The chromosphere was brighter so lost the details visible in the PST black box Vixen mod (0.7A it seems), I assume more light through Bobs filter.
Do try a couple of polarisers to dim it but clouds came over so no chance to experiment properly.

The 127mm will probably be better, from memory, though less convenient to get out.

Andrew.
Last edited by AndiesHandyHandies on Fri Jul 26, 2019 7:39 am, edited 1 time in total.


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marktownley
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Re: 90mm TS Triplet Mod

Post by marktownley »

All good modding!


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