Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by MalVeauX » Mon Sep 30, 2019 10:47 am

MAURITS wrote:
Sun Sep 29, 2019 1:05 pm
What a great review Marty.
In the first place you need for sure the knowledge to make such a pst etalon, looks on the first sight difficult.
The results are awesome.
Thankfully fine folk here on S.C. lend their wisdom, as this stuff isn't really intuitive unless you know what each component is and is doing and that's not really published by the manufacturer.

Next I want to mod the new 10mm blocking filter to also be straight through to eliminate that mirror being in the imaging train.

Very best,



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by george9 » Wed Oct 02, 2019 1:07 am

For the 10mm blocking filter, will you skip whatever the mirror is accomplishing? I am guessing it is redundant with your red CCD filter. E.g., in current Lunts, it passes IR out the system instead of reflecting it up into the eyepiece. Not sure about pre-Meade Coronado, but it is the same team. Not sure exactly what my early pre-Meade blocking filter (Prom15T) mirror does.

George



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Wed Oct 02, 2019 1:22 am

I tested the Coronado BF15 mirror with the spectrograph some time ago and found as you say it's a IR reject mirror.


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by MalVeauX » Thu Oct 03, 2019 1:11 am

Merlin66 wrote:
Wed Oct 02, 2019 1:22 am
I tested the Coronado BF15 mirror with the spectrograph some time ago and found as you say it's a IR reject mirror.
george9 wrote:
Wed Oct 02, 2019 1:07 am

For the 10mm blocking filter, will you skip whatever the mirror is accomplishing? I am guessing it is redundant with your red CCD filter. E.g., in current Lunts, it passes IR out the system instead of reflecting it up into the eyepiece. Not sure about pre-Meade Coronado, but it is the same team. Not sure exactly what my early pre-Meade blocking filter (Prom15T) mirror does.

George
Good points, so if I already have a filter that is rejecting long IR wavelength, it accomplishes the same thing then?

Very best,



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by george9 » Thu Oct 03, 2019 7:24 pm

For imaging I expect it is fine. The red-CCD should cover what the camera should be sensitive to.

For visual, I am just not that well versed in near-, intermediate, and far-IR. The Lunts are very redundant for safety I know (so that, for example, forgetting the blocking filter doesn't blind you). What I understand is:

KG3 covers intermediate and far IR
UV/IR coated KG3 covers all IR
Baader red-CCD covers near and intermediate IR to 1200 but not longer
Baader 35nm H-alpha covers near and intermediate IR to 1200 but not longer

(By the way, I noticed Baader has a disclaimer never to use their 35nm as an internal ERF, not that they say it will fail.)

George



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by MalVeauX » Mon Oct 07, 2019 2:03 am

george9 wrote:
Thu Oct 03, 2019 7:24 pm

(By the way, I noticed Baader has a disclaimer never to use their 35nm as an internal ERF, not that they say it will fail.)
I think, with 99.9% certainty, this is to prevent someone from pointing this filter, at focus, at the sun as a stand alone "Ha" filter thinking it's meant for that and not just a night-time filter. Many use this filter in the light beam, but not at focus, as an ERF and it's the ideal one actually.

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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Mon Oct 07, 2019 6:51 am

Yes,
I saw that .....
As we keep saying solar mods are non standard and should be treated with extreme caution.
We are stretching the envelope.....always opt for the safest option.
I personally think all ERF and sub ERF for H alpha should be Baader D-ERF filters.


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Rusted » Wed Oct 09, 2019 2:05 pm

Marty,

Thanks for your interesting post on the mechanics of PST modification.
If only it were that easy! Then we would all be able to match your exquisite results with the same "kit of parts." ;)

I see you use an aperture stop on your 6" f/8 to provide a true 120mm @ f/10.
My [rather limited] understanding is that a faster [f/8] telescope is self-limiting to f/10 by means of geometry alone.
This being due to the f/10 correction optics of the PST etalon lens group.
They won't allow an angle of incidence larger than an f/10 light cone to pass.

Do you consider is there is any particular advantage to stopping down the objective?
Reduced internal heating perhaps? Stray light reduction?

An internal D-ERF can/should only be placed where the F/8 light cone falls within its clear aperture.
Too near the objective and the light cone will heat the D-ERF supporting baffle and cause vignetting due to annular overlap.

Perhaps the 120mm aperture stop will allow a more forward placing of the D-ERF?
Less intensely focused heat, nearer the objective, due to the larger illuminated area?

Thanks
Chris


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by MalVeauX » Thu Oct 10, 2019 2:56 pm

Rusted wrote:
Wed Oct 09, 2019 2:05 pm
Do you consider is there is any particular advantage to stopping down the objective?
Reduced internal heating perhaps? Stray light reduction?

An internal D-ERF can/should only be placed where the F/8 light cone falls within its clear aperture.
Too near the objective and the light cone will heat the D-ERF supporting baffle and cause vignetting due to annular overlap.

Perhaps the 120mm aperture stop will allow a more forward placing of the D-ERF?
Less intensely focused heat, nearer the objective, due to the larger illuminated area?

Thanks
Chris
Hey Chris,

The thermal load alone is a consideration. If I left it 150mm F8 and just reduced to F10 at the collimating lens, the thermal load is that of a 150mm still in the tube at least (not the same at focus of course). I think it also matters for focus, but only by a little bit, and the collimating lens is rather specific, my understanding is that the angle of the rays of light are different at F8 than at F10 in the same -200mm position, but I'm not well versed enough to really speak to it beyond that, or I think everyone would avoid cutting their OTA tubes and just let the collimating lens do the F10 thing, but I don't think its that simple.

Very best,



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by marktownley » Thu Oct 10, 2019 7:38 pm

Rusted wrote:
Wed Oct 09, 2019 2:05 pm

Do you consider is there is any particular advantage to stopping down the objective?
Stopping down an objective also reduces spherical aberration. There will be less Spherical Aberration with a 150/8 stopped down to 120, than with a 120/10 operating full aperture.


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Rusted » Fri Oct 11, 2019 4:18 am

Thank you both for your responses. I shall try stopping down my 150/8 H-a 'scope.

Though an umbrella might be a better mod given our present run of wet weather. :roll:


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by bart1805 » Sun Oct 13, 2019 8:15 pm

MalVeauX wrote:
Mon Sep 30, 2019 10:47 am
Next I want to mod the new 10mm blocking filter to also be straight through to eliminate that mirror being in the imaging train.
With the Coronado BF's, the part with the valuable BF is not threaded, it is just glued to the bottom of the eyepiece holder. First remove the BF itself. Then use heat to loosen the glue and you will be able to pop the piece out of the holder.
With Lunt BF's it works basically the same. But the Lunt piece has a T2 thread you can use.



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by MalVeauX » Mon Oct 14, 2019 1:22 am

bart1805 wrote:
Sun Oct 13, 2019 8:15 pm
MalVeauX wrote:
Mon Sep 30, 2019 10:47 am
Next I want to mod the new 10mm blocking filter to also be straight through to eliminate that mirror being in the imaging train.
With the Coronado BF's, the part with the valuable BF is not threaded, it is just glued to the bottom of the eyepiece holder. First remove the BF itself. Then use heat to loosen the glue and you will be able to pop the piece out of the holder.
With Lunt BF's it works basically the same. But the Lunt piece has a T2 thread you can use.
Thanks!

Prior to this I had attempted to gently unthread it, but it didn't budge so I didn't force it until I found more information. I will have to try this soon.

Very best,



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by daslolo » Thu Feb 20, 2020 11:26 am

Would a 2" 2x barlow at the focuser of a f/5 refractor effectively turn it in a f/10
Then slide in the PST mod

Like this one https://www.amazon.com/dp/B07BRLT4LB/re ... tEb17Y1QZQ


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Thu Feb 20, 2020 12:40 pm

Daslolo,
Probably not. The standard PST mod needs the etalon to be at -200mm inside the focus. Don't think you'll achieve that spacing with a normal Barlow.
You could replace the front lens of the PST assembly with a shorter negative focal length lens....


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by daslolo » Sat Feb 22, 2020 3:57 am

Merlin66 wrote:
Thu Feb 20, 2020 12:40 pm
Daslolo,
Probably not. The standard PST mod needs the etalon to be at -200mm inside the focus. Don't think you'll achieve that spacing with a normal Barlow.
You could replace the front lens of the PST assembly with a shorter negative focal length lens....
So a negative focal length lens would also turn the convergent rays parallel to go inside the etalon like a plano-concave lense?
And where do I find such thing.
Also where do we find adapters between various M? M32 to M42 female female is my current quest :)


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Sat Feb 22, 2020 4:17 am

AOK Swiss supply a 2" to M50 male nosepiece which fits the PST etalon assembly and a rear adaptor M50 female to 2"
http://www.aokswiss.ch/index_sonne.html
Edmund Optics probably have a suitable negative lens...you're looking for a 25mm diameter, negative focal length = 20 x focal ratio i.e. for an f5 scope use a -100mm fl at -100mm inside focus.
https://www.edmundoptics.com.au/p/250mm ... lens/5538/


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by daslolo » Sat Feb 22, 2020 8:34 pm

Merlin66 wrote:
Sat Feb 22, 2020 4:17 am
AOK Swiss supply a 2" to M50 male nosepiece which fits the PST etalon assembly and a rear adaptor M50 female to 2"
http://www.aokswiss.ch/index_sonne.html
Edmund Optics probably have a suitable negative lens...you're looking for a 25mm diameter, negative focal length = 20 x focal ratio i.e. for an f5 scope use a -100mm fl at -100mm inside focus.
https://www.edmundoptics.com.au/p/250mm ... lens/5538/
Thanks Ken, where is the adapter that houses the lenses on a 2" tube? (M50 i guess)

You have a spectroscope, what's the reading on the costing of the pentaprism in the PST?

And this double layer filter cube lodged before the eyepiece?
Double layer filter
Double layer filter
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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Sat Feb 22, 2020 10:40 pm

Daslolo,
The PST etalon assembly with the M50 thread front and back is used with the AOK swiss adaptors. The 2" nosepiece mounts to the telescope and the 2" rear female is used to add spacers and final blocking filter.
The pentaprism seems to be AR coated.
The small red filter you show is the final narrowband sort filter. There should be a highly reflective filter element (ITF) at the inner end of the eyepiece holder - this acts as an erf. The combo of the ITF and final sort filter makes up the "blocking filter" assembly.


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Sun Feb 23, 2020 1:17 am



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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by daslolo » Sun Feb 23, 2020 9:50 pm

Thanks Ken.

I'm only modding the black box out, for now.

The pentaprism offers added protection, so be mindful of that when modding. I know it because I could feel something in my eyeballs in the mod, then nothing when I put back the stock PST. Through binos so I'm halving per eye exposure which means the penta must reduce exposure by a LOT.
In this context Diane's blog is important.
This Diane blog got me reading some science yesterday night! Our tolerance to IR isn't bad, decay seems slow and can be felt. Diane's numbers are missing the /cm2 so they're not useful out of the context of her blog, they only provide a ratio of blocking with and without the BK filter. This filter I'm not seeing in any of the mods, why is that? Have you guys measured the actual output after mod?

What's a narrowband "sort" filter? Couldn't find anything on sorting light.
Why is it made of two layers: one golden reflective and one red block?
Is the gold the ITF (metal deposit)? ref: https://luntsolarsystems.com/equipment-care/
Is the ITF a blocking filter, is ITF = BF?
It's tiny, about 4mm across, does it mean the PST is rocking a B400, is that what B stand for in the lunt and coronado diagonal (Blocking)?
And why is the ITF in the diagonal and not in front of the etalon to protect it from heat and UV, from decay.
What is the other filter that's about 17mm in diameter which is in the tube that's holding this eyepiece holder? Is it the ERF like those expensive Baader everyone talks about?

Pedro's youtubes are only slideshows, I didn't find any value in it. Value is in understanding why things are where, or for those who can't be bothered with that, where to get the parts.


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Sun Feb 23, 2020 10:07 pm

Daslolo,
""What's a narrowband "sort" filter? Couldn't find anything on sorting light.""
The etalon produces a "comb" of light across the whole spectrum....each "tooth/ peak" section about 0.7A wide and separated from it's neighbour by 10A. One of these "tooth/ peaks" is very close to H alpha, and to suppress all the others while just letting the H alpha go through is the job of the final sort filter. It has a bandwidth less than the separation.

"" What is the other filter that's about 17mm in diameter""
This is the ITF filter ( induced transmission filter) which was introduced by Coronado when they changed design away from the original ERF coated objective. It acts as an ERF, protecting the final sort filter.

On PST mods, to reduce the incoming energy before the etalon, an effective ERF should be fitted to ensure adequate safety.


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by daslolo » Sun Feb 23, 2020 10:51 pm

Thanks again Ken, I am starting to understand how it all works now.

It seems that adding another sort filter could narrow the total bandpass of the scope even more if, by gambling on manufacturing tolerance, its band is slightly offset from the other sort filter.
Is it the red part of the cube or the golden? why is the cube made of two layers?
Is it also called a blocking filter or BF or B400?

I'll get an ERF. Which ones have you spectrum analyzed which provides acceptable protection and does't cost 300$ for a 2"?

I'm doing the rock bottom pricing here, while being fully aware that I have only 2 eyeballs, because, from the parts I've gathered, a Mod black box is not sensible when compared to the price of a lunt50/B400 (only for the fun of making it and learning), a full mod where the PST turns into an eyepiece is where it starts to make sense.
But in that last scenario, as Marty said in another thread, a Quark is cheaper and narrower (more contrasty?)


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by Merlin66 » Sun Feb 23, 2020 11:14 pm

The blocking filter designations (BF 10/ BF15/ B600 etc refer to the whole blocking filter assembly i.e. including the ITF or pre-filter (in the Lunt Schott BG38)
The number is generally the clear aperture of the final sort filter - BF10 = 10mm. B600 = 6mm etc.
To achieve the required sort filter bandwidth (around 8A) requires a sophisticated filter design...
Narrowing the bandpass is usually done by doubling up on the etalon, two 0.7A etalons will get the bandwidth down to around 0.4A -0.5A.
I'm not a fervent supporter of using sub-diameter ERF's.
The Baader H alpha 35nm CCD filter has the same coating as the Baader D-ERF.


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Re: Easy PST Module with ERF (non-destructive, no cutting of OTA, & no-black-box rebuild)

Post by daslolo » Mon Feb 24, 2020 2:36 am

Merlin66 wrote:
Sun Feb 23, 2020 11:14 pm
The blocking filter designations (BF 10/ BF15/ B600 etc refer to the whole blocking filter assembly i.e. including the ITF or pre-filter (in the Lunt Schott BG38)
The number is generally the clear aperture of the final sort filter - BF10 = 10mm. B600 = 6mm etc.
To achieve the required sort filter bandwidth (around 8A) requires a sophisticated filter design...
Narrowing the bandpass is usually done by doubling up on the etalon, two 0.7A etalons will get the bandwidth down to around 0.4A -0.5A.
I'm not a fervent supporter of using sub-diameter ERF's.
The Baader H alpha 35nm CCD filter has the same coating as the Baader D-ERF.
So one more zero in the BF nomenclature = one less zero of diameter :? BF30 is 30mm?

I see Baader is the reference, ever tested cheaper filters?
I think that's the one. So I'd put that or the 1.25" version in front of the 20mm colimator lens in a full mod setup.
baader.png
baader.png (504.35 KiB) Viewed 5385 times
What about that one?
https://www.firstlightoptics.com/uv-ir- ... ilter.html

Re: combing the spectrum, now it matches what I've seen, I took out the blocking filter assembly to find the focal point and saw a blue green sun on the piece of cardboard. Those green and blue spikes are the harmonics uh.


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