PST modification on F/10 MAK

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DSobserver
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PST modification on F/10 MAK

Post by DSobserver »

hello guys

I'm with some solar friends and were talking about PST mod.

Why no one already made PST mod using a MAK scope.
At least we're already at F/10 so theoretically it should work, isn't it?

Any idea?


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Re: PST modification on F/10 MAK

Post by Merlin66 »

Two reasons:
The concern about heat affecting the secondary - depends on how good your ERF is - finding one big enough may be expensive!
The second is ensuring you can get enough backfocus to fit the PST etalon onto the rear cell.
You need to be able to focus 200mm behind the rear cell...
If these two issues are addressed than no reason why not.....


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Re: PST modification on F/10 MAK

Post by marktownley »

My big concern would be heat on the secondary mirror spot, even with a full aperture ERF in place, I think the mirror spot is just glued on - I can imagine glue melting / cracking.


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Re: PST modification on F/10 MAK

Post by DSobserver »

My big concern would be heat on the secondary mirror spot, even with a full aperture ERF in place, I think the mirror spot is just glued on - I can imagine glue melting / cracking.

well in my case it is an intes mak so not glued....and already F/10 ;)


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Re: PST modification on F/10 MAK

Post by marktownley »

fair enough then ;) Let us know how you get on...


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Re: PST modification on F/10 MAK

Post by DSobserver »

I'll first check backfocus....


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Re: PST modification on F/10 MAK

Post by colinsk »

My big concern would be heat on the secondary mirror spot, even with a full aperture ERF in place, I think the mirror spot is just glued on - I can imagine glue melting / cracking.

While I have noticed solid etalons heating in the sun I find it is only a few tenths of a degree. It is enough to make sure you track the sun for the entire session. I don't think a Baader ERF lets in enough light to melt glue. The next time I have one on loan I will make an energy measurement. I don't have plans to have one anytime soon though. :dry:


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Re: PST modification on F/10 MAK

Post by DSobserver »

:cheer: Just tried guys!

It works easily :woohoo:

No back focus issue. Sky was not perfect enough to judge the quality but it's definitely an interesting mod with big diameter but easily transportable (cause with 125 f10 scope.... :X )


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Re: PST modification on F/10 MAK

Post by Merlin66 »

Sounds very promising!!!
Any chance of some photos, of the set-up and the results???


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Re: PST modification on F/10 MAK

Post by DSobserver »

I finally take time to post a picture from this setup



Unfortunately weather was not good enough to deeply test this mod, but we could achieve focus with Ha sun.

Next step is now to invest in my own ERF..... B)


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Re: PST modification on F/10 MAK

Post by oldfield »

I did it with a C5 before and it works out well.


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Re: PST modification on F/10 MAK

Post by marktownley »

Maybe there's hope for my ETX90 yet...


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Re: PST modification on F/10 MAK

Post by DSobserver »

remember in may my trial? :whistle: Now it become reality! :evil:





And it works perfectly guys with or without PST black body!


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Re: PST modification on F/10 MAK

Post by marktownley »

Way cool! Any pics taken through it?


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Re: PST modification on F/10 MAK

Post by DSobserver »

no man, I'm only visual guy for the moment...


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Re: PST modification on F/10 MAK

Post by brianb11213 »

Just one thought, since the ERF is sitting right across the front of the tube, you could stick an opaque spot onto the centre to shelter the secondary mount from "direct" solar radiation transmitted through the ERF, without having any effect whatsoever on the optical performance. The more concentrated beam hitting the secondary mirror after being reflected from the primary would be largely reflected rather than absorbed so shouldn't heat the mirror much.

The way I understand Maks (and SCTs) the backfocus design position is unlikely to be as much as 200mm behind the rear port, going too far from the design back focus can cause serious issues with spherical aberration correction which is calculated for a fixed back focus, the working focal length will be changed if you can actually get to focus and with some Maks in particular (the Eastern European ones) going beyond the rated back focus starts to cut the aperture by shadowing the outer part of the primary with the baffle tube. How about sticking a Barlow in the rear port & using it to project a f/20 beam? That way you could get the 20cm distance without stretching the backfocus ...


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Re: PST modification on F/10 MAK

Post by papamidnight »

Nice work, what ERF are you using?


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Re: PST modification on F/10 MAK

Post by DSobserver »

I just try with a 1.6 barlow (so f/16) and....it doesn't really works : Ha area became really small so without interest.

At the opposite your idea to stick an opaque spot is a good idea, but I'm afraid that glue will damage coating when I want to remove it. Don't you think?

Papa, my ERF is a D-ERF from baader 5 I don't think that someone else is producing them in this diameter (135mm)


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Re: PST modification on F/10 MAK

Post by Merlin66 »

Hmmm
You must remember the etalon need to be "held" at the -200mm position.
So any barlow etc added after the etalon needs to be focused without touching the main focuser on the scope.
I don't think you'll have any issues/ problems with the Mak secondary.


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colinsk

Re: PST modification on F/10 MAK

Post by colinsk »

Hmmm
You must remember the etalon need to be "held" at the -200mm position.
So any barlow etc added after the etalon needs to be focused without touching the main focuser on the scope.
I don't think you'll have any issues/ problems with the Mak secondary.

We do have a little bit of slop in this number. Moving the etalon will either make the center red shifted and the outside blue shifted or the reverse. The best across band view will be close to -200mm.

The goal of collimation is to make the rays as close to perpendicular to the etalon mirrors as possible. Because the sun is .5deg wide it fails.


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Re: PST modification on F/10 MAK

Post by peter drew »

I trialled a 5" SCT with a full aperture Daystar ERF, there was no back focus issue and for the limited period of use no heating problems were noticed. I was disappointed with the visual results compared to the same ERF on a 5" F10 refractor so the experiment is currently shelved, I might revisit it in the future as the compactness is attractive. :)


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