Easy Peasy PST Mod

[StarryDave]

I have just finished my first solar season with my PST mod which this group helped me to build. It seems to work very well and you can see a compilation of my captures at https://youtu.be/q2_tTYrpWwQ

The mod is very simple and here are the steps:
1. Remove original 40mm PST objective.
2. Mount 2" Baader 7nm Ha filter to front of PST using 52>48mm step down ring.
3. Mount F10 OTA over PST tube to focus at 200mm past etalon.

I tested the concept using a Celestron Powerseeker 70AZ OTA. I had to remove the last baffle which just pushes out but I did not have to cut the tube.
Once concept was proved I then used a Celestron Cosmos 90GT OTA for the final configuration. Again, baffle removed and tube not cut. Below are some fotos to show the design.

PST90 tuner side.png (1.46 MiB) Viewed 1387 times

PST90 focus side.png (1.53 MiB) Viewed 1387 times

PST90 overview.png (1.03 MiB) Viewed 1387 times

[marktownley]

Nice mod!

[thesmiths]

This interesting configuration could in principle also be used for the CaK PST. The 40mm optics is not as much of a limiting factor at the shorter wavelength, but it's probably a quick and easy way to get 70mm to 80mm aperture. The CaK PST has a quite nice bandwidth (I think a little better than the Lunt CaK).

[highfnum]

very nice!

[cybermayberry]

That is great

[Mrural]

Hello - Can I use a 2" Lumicon LF3090 filter for this mod? I can't seem to find passband info on it? Please advise. Thank you.

[marktownley]

Hello - Can I use a 2" Lumicon LF3090 filter for this mod? I can't seem to find passband info on it? Please advise. Thank you.

Not much info out there on it. Is it a coloured glass type filter or does it have a dichroic coating?

[Mrural]

Thanks for the reply - looks like a colored filter to me. I think I'll just keep on the lookout for the Baader filter.

[Flying dinosaur]

Forgive my ignorance, but am I correct in reading this basically converts a 40mm objective to a 90mm objective, giving much better resolution and “simply” moves the etalon further back in the light path? If so, what a neat idea! I had heard that some of the solar scope manufacturers were doing something like this…but had no clue folks were trying that on their own.

[StarryDave]

The AOKswiss website http://www.aokswiss.ch/ayo/pst.html states that

A simple way to protect the filter is to use a good normal red filter with 48 mm thread (as for a 2" eyepiece). This works up to max. 4" scopes and f : 10 (mounting on the adapter).

I think this means that you may be able to use the Lumicon if your objective is smaller than 4".

I have been using my mod with the Baader filter for a few months now and it seems to work fine with no problems. You can see some of my solar animations I made with it here : http://starrydave.com/?page_id=1330

[marktownley]

Thanks for the reply - looks like a colored filter to me. I think I'll just keep on the lookout for the Baader filter.

Sounds sensible to me

[StarryDave]

Forgive my ignorance, but am I correct in reading this basically converts a 40mm objective to a 90mm objective, giving much better resolution and “simply” moves the etalon further back in the light path? If so, what a neat idea! I had heard that some of the solar scope manufacturers were doing something like this…but had no clue folks were trying that on their own.

That's the idea. I removed the stock 40mm objective and replaced it with a 90mm f10 OTA. I now have a 90mm f10 h-alpha scope that cost less than £1000. Also, my design means that the PST and donor scope are undamaged and can be easily restored to their original condition.