PST mod options and questions

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MalVeauX
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PST mod options and questions

Post by MalVeauX » Sun Mar 17, 2019 11:24 pm

Hey all,

I'm tinkering around with a few things, just trying to figure a few out and have some questions. I have an old PST that I've dissembled. The front objective is cloudy, but it still puts up a fine image and has good contrast. But, that probably could be better, is my understanding. It's an old PST so the ITF is the objective. It has a little 5mm blocking filter in the eyepiece and that's it. Not too much concerned with visual here though. I have the front & rear adaptesr from AoK Swiss to use as a PST mod and I've used it in a few different configurations. However, I'm starting to explore basic Stage I & Stage II type PST mods as I have no experience with that.

C8 Edge HD:

I have tried doing a Stage I PST mod with my C8 Edge. I removed everything from the back of the C8 Edge and put a 2" visual back. I insert the PST with the front AOK swiss adapter (removed the gold tube and objective). I can't seem to find focus anywhere with it. I've wracked focus on the C8 Edge back and forth, but didn't find focus. Not sure if there's something I'm missing. It could be that the C8 Edge doesn't have enough focus travel on the mirror for this to work? Not overly concerned, was just experimenting really to see how my PST etalon performed. Ideas?

Solarmax II 40mm Double Stack:

I'm curious about the Solarmax 40mm double stacked onto the PST. Does the PST have to have it's front objective for this? Say mine is cloudy/rusted as it's old, couldn't I just remove the objective lens and put the Solarmax 40mm in front, threaded in as normal? I imagine it has it's own objective lens too since it can be used with a blocking filter on a scope, right? So the objective in my old PST really has no purpose if I put a solarmax 40 on the front of it, right? Might increase contrast due to removing the rusty/cloudy red objective?

80mm F5 Achromat as PST Mod Stage II:

If my PST front objective is going to rust over and I want to maintain a full disc option from my PST etalon, and have the option to double stack it, couldn't I just do a PST Stage II mod with a 400mm achromatic refractor, stop it down to F10, and basically just make a better PST mechanically? The idea would be to maintain a full disc option with the same 40mm F10 scope as the PST but friendlier to imaging.

I was thinking of getting a Meade Adventure scope (80mm F5) and stopping it down to 40mm F10. PST Stage II mod it. And then have an adapter plate made to allow the solarmax 40mm II etalon to be mounted in the front. That solarmax etalon objective would serve as the ERF or ITF for the PST etalon right? Or do I need a UV/IR filter or ERF in front of the first PST etalon? And if my understanding is correct, I have to cut away 200mm of the focal length of the OTA on the donor scope, so the Meade Adventure scope at 80mm F would be a tiny little thing left over. Do I also take into consideration the length of the focuser? Or is it just 200mm from the OTA tube and then put the focuser back on? Then insert PST etalon with front & rear adapters? I will need extensions behind this too though, correct? Is it another 200mm or does it take into account the blocking filter or anything else in the total pathway? I've seen some that were less than 200mm after the etalon, such as 140mm?

Thanks!

Very best,

bart1805
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Re: PST mod options and questions

Post by bart1805 » Sun Mar 17, 2019 11:44 pm

C8: did you use the etalon with or without the lenses? I would try with the lenses. But I think the C8 has to little back focus to be able to position the etalon 20 cm before the original focus position.
Solarmax: it is just an etalon, not a lens! So yes, you definitely need your original PST lens.
PST Mod Stage 2: I would try and find a replacement for the clouded PST lens. Apollo had one for sale a couple of days ago. Why bother with different scopes?
Then I would order a PST thread to SCT adapter, AOK made one for me about two years ago. The PST thread is close to SCT thread, so you could experiment with Loctite55. Attach a low profile SCT focuser and off course a Coronado BF.
It will look a bit like this, includes the adapter:

https://www.astroforum.nl/filedata/fetc ... 1496008339

The golden tube is a 60mm Denkmeier Mod.

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MalVeauX
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Re: PST mod options and questions

Post by MalVeauX » Mon Mar 18, 2019 12:05 am

Heya,

Yea, used the collimating lenses in the etalon. Not sure if the blackbox focuser needs to be in a certain position first and then wrack focus on the donor scope's focuser or what. I just tried focusing a few times in and out through its range and didn't see anything other than the smear on the camera.

Thanks for the info about the solarmax 40, just being an etalon. That helps avoid a lot of big oopsies!

Was just thinking down the road if my PST objective continues to cloud up. I'll either get a replacement if I find one harvested. I still get a contrasty image out of it. If it completely goes though, was just thinking of a way to replace the scope itself and just keep the etalons.

Very best,

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