PST modders - questions

[b16707]

As I was looking for eyepieces for my PST Coronado, I came across the fact that you can mod stage 1 or 2 for this scope. I personally love modding things so naturally this got me very intrigued especially since it seems reversible also.

I was wondering:
1. Does a stage 1 essentially replace the golden tube for something with more power + erf? Thus equating more zoom and closer views of the sun? Maybe more aperture for brighter images too? Is my understanding here correct?
2. michael8554's mod (https://stargazerslounge.com/topic/192216-my-70mm-pst-stage-1-mod/) seems to be the most cost effective one ive seen so far in my 1 day of researching. What are people's suggestions here? Would a more expensive scope yield sharper/better quality results? Ive seen some mods that cost $1k+ which wouldnt i be better off just getting a 60mm solarmax or something?
3. Is my understanding that a stage 2 mod only keeps the etalon? 

Now im super glad I got the PST. There looks to be so many potentials. I want to use it for photographing the sun. In its current stock state it seems ok but thinking it could be better.

[Peter Drew]

A stage 1 mod essentially involves substituting the original 40mm objective with one of larger aperture. The new larger aperture will require an additional energy rejection filter to help protect the rest of the unit from the increased energy input. This can either be a full aperture front filter big enough to fully cover the objective or a smaller version placed inside the OTA further down the light path, the latter is less expensive. The stage2 mod dispenses with everything except the etalon and the ITF/blocking filter module. The donor objective ideally needs to operate at F10 as this is the configuration for the etalon design.

IMO, the smallest aperture really worthy of a mod is 80mm, it's exactly the same principle with larger apertures and there are many suitable ones at reasonable prices. There is no comparison between a large mod and the regular 60mm dedicated models, the larger mod provides much more resolution and has a brighter image that stands higher magnification. I operate a 150mm F10 stage2 mod and couldn't be more pleased with the performance.   ?

[paulastro]

I can vouch for Peter's 150mm Mod, for high power work and for incredible detail in the proms and surface detail it would be hard to be.  Mind you, my ideal set up would be Peter's mod AND the double stack 60mm Lunt I used to own for whole disk low power views.

[b16707]

Thanks guys! excellent info

@Peter Drew do you have a link to your build that i can check out? 150mm for a suitable ERF that size seems $$$$$

Seems like alot of waste to dump everything but the etalon and the filter. You cant get these parts separately cheaper than buying a full PST to start with (im going to guess no haha)?

[Merlin66]

Drop me an email address and I'll send you a copy of my PST Mod pdf.

A longer focal length "donor", say 100mm aperture, f10 (=1000mm focal length) also really needs a larger blocking filter assembly (around 10 to 15mm) than the one built into the PST (5mm).

Unfortunately PST mods are not cheap, but neither is the alternative.

 

[b16707]

@Merlin66 i read somewhere where your name was dropped too, forgot where. Will PM you. Thanks!

@michael8554's mod that i mentioned in my original post at £176.30 i would consider as very cheap. Any drawbacks of his setup? 

I just have no idea what im looking for right now. Would i need an expensive refractor or a cheapo one is probably my main question. Would one have advantages optically over another.

 

 

[Moonshane]

You don't need an expensive refractor as at F10 almost all on the market today would be fine. The only downside of the 70mm is that the resolution reduces with aperture.

I have a 100mm stage two mod which I use with binoviewers. I once made a 60mm objective to fit it. As above there's no comparison with the views compared with the 100mm. Peter's 150mm is something special. I generally use 68x or 86x roughly in mine. Peter's mine I think is 150x.

 

 

[Merlin66]

I'm currently using a TS102 f11 with a full sized D-ERF with my PST Stage 2 mod. The rear end is interchangeable with a Baader Cool Herschel wedge.

Works well.

[Rusted]

I was turned on to H-alpha on this forum so might as well stick my oar in.

Be prepared to spend a lot more money than you ever imagined.

First I spent hundreds of pounds on a secondhand PST just for the vital etalon and rejection filters.

There must be a lot of dodgy PSTs knocking round at the moment being unloaded by equally dodgy sellers flogging cloudy filters.

Be prepared to struggle really hard to separate the vital PST components without damage. Most bits are sealed with a thread locking compound!

I have a lifetime of practical experience including mechanics, restoration and even plumbing.

The PST almost found my limits using approved tools. I almost broke the rubber strap wrench using extra leverage.

The PST's rejection filter was [typically] clouded over so that had to be replaced too by a Maier from the USA. More money!

I used an old 150/8 Celestron refractor and added the PST bits on the end. It converts automatically to a 120mm F10.

No extra expense but you just lost 30mm of clear aperture which you thought you'd paid for and still had to mount a great big lump of telescope.

So why not choose a smaller F10 in the first place? 100mm f10 is a nice place to be.

Now I needed a 90mm Baader DERF half way down the telescope tube for many hundred of pounds more to protect the PST bits and my eyes.

Getting the PST components at the precise measurement is VITAL and will cost another arm and a leg.

Prepare to lash out on umpteen spacers, T2 conversions and shallow, helical focusers.

The high powered views of prominences and surface detail are really quite amazing.

Though I was never able to use the bare PST for comparison due to the VERY obvious filter clouding.

Then other projects got in the way before I was able to provide binoviewing at even greater expense.

The downside IMO is that very high magnifications are unavoidable as F10 optics increase rapidly in focal, length with increasing aperture.

Larger instruments @ f/10 and high magnifications need a really sturdy mounting too. 

My advice is to think VERY carefully about your budget and what this will means in terms of aperture.

You can't leave ANYTHING out of the ABSOLUTELY VITAL filter chain unless you really want to be instantly blinded!

There's absolutely no shame in being [relatively] poor and proceeding with rather more modest but achievable plans.

Unfortunately my own history is one of endless white elephants but I have a lot of fun along the way.

 

[Merlin66]

Just a comment....

A good PST makes a good mod.

Unfortunately not all PST etalons are the same. The 10/80/10 rule applies - 10% should never have left the factory, 80% are OK, just and 10% are outstanding. Finding a very good PST etalon can take some time and effort.

 

[Peter Drew]

Yes, PST mods are not cheap, just cheaper. My 150mm mod cost me around £2000. Look up the price of a Lunt 152mm solar scope!    ?

[Moonshane]

Here's a couple of links that may help

 

 

 

 

[Paul73]

Here is my 100mm stage 1 mod.

As mentioned, getting the PST apart was a real struggle. I ended up drifting straight through the gold tube to get it off! It is still used in PST form when I need to be portable.

I find that it is an absolute Prom machine, outdoing many of the amazing images that we see on this forum. That is where the larger objective comes into its own. However, the surface detail doesn’t seem as good as a Quark or a Double Stacked smaller Ha Unit (Maybe, I’ve done something wrong).

You are certainly asking questions in the right place. I would have certainly either, not even tried, or messed it up badly, if it were not for the advice received on this forum.

Cost? I sourced everything 2nd hand, which took a while). £500(ish) plus the PST.

Paul

[b16707]

thanks for the updates all!

In reading through the mods needed, it doesnt seem as daunting as some say it is. with Merlin's PDF/doc, it bring it down to laymans terms really.

Im curious if the PST i got is of a good one or bad one. It was brand new sealed and i got it for an absolute steal at a price that i have never seen it go for even on a used forum. At its stock config right now with stock eyepiece, it seems to give pretty nice and sharp views of the sun, flares, etc.

In terms of overall expense, it doesnt seem THAT expensive to do a stage 1 at least. Cheap refractor, somewhat pricey ERF, a couple of cheap tubes. That seems to be it. I understand that everyone's idea of expensive is different but when compared to a $3000+ solarmax vs a <$1000 stage 1 mod, i think its very very reasonable. I do think a stage 2 is better for me as the 5mm blocking filter on the PST (5mm right?) seems a bit small and hard to view with so that will up my $ a hefty bunch...erf+bf10/15 being the biggest costs

or if the costs to mod nets out the same as getting a big ERF for my 8in SCT and a couple of blocking filters for that, then i might as go that route. Or selling my 8in for a 6in and stepping that down if there is a erf for a 6in. Having less junk in the house seems enticing for sure. Still researching....

[Moonshane]

I may be wrong (as I have no idea how to mod an SCT for ha solar) but you'd need an ERF, plus a blocking filter of 20mm or more for a 2000mm focal length. I think the nearest is a 30mm and these come to about US$1500. That said, the views would be great I'd think if it was possible. Maybe a Quark would be better for an SCT naturally with a suitable ERF on the outside of the objective.

[b16707]

I havent done the research myself yet but there have been people who have done it. Theres this guy selling his gear but I dont have a scope that size to use it.
https://www.cloudynights.com/classifieds/item/143597-build-your-own-daystar-ha-solar-scopes/

The views may be awesome, but could maybe be too zoomed in for me now that im thinking of it. Who knows, never tried it.

[Merlin66]

Over on the Solar Chat forum you'll find examples of the PST mod applied to SCT's.

There are a couple of vendors who have designed and sell a multi wavelength ERF (CaK, MgIII, Ha) for the SCT.

https://solarchatforum.com/

[b16707]

found out about the daystar quark. maybe i dont need to do any mods and another PST will be for sale =D.