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

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Re: PST, how to replace that black box?

Post by MalVeauX » Mon Sep 09, 2019 9:49 pm

The 2" -> M36 adapter came in today, so the helical focuser can now sit in a 2" extension. Everything works and focused up nice.

Success!
PST_NoBlackBox_01_09092019.jpg
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PST_NoBlackBox_02_09092019.jpg
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PST_NoBlackBox_03_09092019.jpg
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PSTNoBlackBox_SetupSolar_09092019.jpg
PSTNoBlackBox_SetupSolar_09092019.jpg (109.06 KiB) Viewed 247 times
Very best,

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Re: PST, how to replace that black box?

Post by MalVeauX » Tue Sep 10, 2019 12:45 am

From right to left:

PST Etalon ->AOK Swiss rear PST adapter (2" barrel) -> 50mm 2" Extension -> M36 -> 2" Adapter threaded to a M36 threaded helical focuser -> 1.25" eyepiece nose with ITF threaded inside it -> M33 to M28 adapter -> PST eyepiece holder with 5mm blocking filter inside ->

Those items happened to hit the magical 8" roughly. The helical focuser does the rest.

The camera focuses as you see here.

To use it visually, I add a 2nd 1.25" eyepiece nose to the eyepiece inserted to give it another few mm to achieve focus.

Since I can control in focus range, I can probably get this to work with binoviewers (though is probably too much for that helical focuser). Also, no special low profile adapters or anything needed for the cameras. Seen here is an ASI290MM with its standard 1.25" nose. Since we can control the focus ranges, we can probably get any camera to come to focus, even a dSLR (not doing that thought!).

PSTNoBlackBox_Focus_Camera.jpg
PSTNoBlackBox_Focus_Camera.jpg (94.78 KiB) Viewed 245 times

So, the option where I just have the PST with no black box and potentially still double stack it, works. So that's good. I can at least do this and put a SM40II on it without the internal prism and janky focuser. The helical is plenty precise for this imaging train and course image scale.

The next thing is to diassemble and extend the collimating lens out for use in another scope as a PST Mod.

I will also test it in my SCT with its D-ERF just to show a Stage II PST mod on the SCT that is straight through.

Very best,
Last edited by MalVeauX on Tue Sep 10, 2019 1:04 am, edited 1 time in total.

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Re: PST, how to replace that black box?

Post by MalVeauX » Tue Sep 10, 2019 12:46 am

Questions:

Are there any special coatings or ERF properties to the blue newer PST objective lenses?

Does a PST etalon need a particular ERF at all at 40mm aperture other than maybe a UV/IR block filter?

Very best,

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Re: PST, how to replace that black box?

Post by Merlin66 » Tue Sep 10, 2019 1:45 am

The blue PST objective is just AR coated - no ERF qualities.
No need to add and upfront ERF etc with the 40mm aperture, the ITF at the rear is all that's required.
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Re: PST, how to replace that black box?

Post by bart1805 » Tue Sep 10, 2019 9:20 pm

A set-up like this is quite ideal to check if the primary of for example your C8 is focussed the way it should with a PST mod. Just connect the train (the etalon and everything after that) and focus with the primary.

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Re: PST, how to replace that black box?

Post by MalVeauX » Wed Sep 11, 2019 11:34 am

Thanks all,

Interesting, I will try it out and report.

So the ITF is effectively the ERF in a system with small aperture that doesn't need an ERF (say 40mm aperture).

So I could also plug this directly into my ST80 stopped down to 40mm with no ERF with some extensions in front and eliminate the gold tube and objective? And then it would be a HA module that just slides in for full disc...

I wonder what the max aperture would be that the ITF can then handle?

And in a system with an ERF, the ITF is not needed, right?

Very best,

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Re: PST, how to replace that black box?

Post by MalVeauX » Wed Sep 11, 2019 4:13 pm

Heya,

Got some testing in this morning.

I tested imaging straight through with the stock PST element and golden tube, and the replaced black box with the straight through design using the stock ITF and 5mm blocking filter. I used an ASI290MM camera so I had to do a 2 panel mosaic for the full disc. I was able to generate a flat field using a cereal bag over the front element. I didn't want to use IMX178 or similar sensors due to the weird grid patterns they produce in HA and the sensor is bigger than the blocking filter's diameter so I didn't want to fool with that again. Transmission was decent at 0.6ms 0 gain.

PST_StraightThrough_09112019.jpg
PST_StraightThrough_09112019.jpg (68.37 KiB) Viewed 213 times
PST_FlatFrameCalibration_CerealBag.jpg
PST_FlatFrameCalibration_CerealBag.jpg (49.74 KiB) Viewed 213 times
PST_StraightThrough_ITF_5mmBF_Transmission_SingleStack_ASI290MM_09112019.jpg
PST_StraightThrough_ITF_5mmBF_Transmission_SingleStack_ASI290MM_09112019.jpg (75.75 KiB) Viewed 213 times
Image

The next project is to extend the front collimating lens forward and use it in a refractor without cutting the OTA. I will test on my ST80 stopped down to 40mm first, as no ERF is needed there, just the ITF. But after I get a Baader Red CCD imaging filter, it will serve as the ERF and I will see about testing it on larger aperture refractors (I have up to 150mm).

To finish out this morning's tests, I also wanted to revisit the PST mod with the C8 SCT and Aires D-ERF. As Bart pointed out, it would be at the F10 focus point of an SCT in this configuration so I tried it out. I removed my crayford focuser and just used a 2" visual back. Inserted the AOK swiss adapters on both sides of the etalon and put it into the visual back. 8" back from there to my helical focuser and ASI290MM camera. Focused the primary mirror to focus. Used the helical inline to my camera to fine focus. Worked great. It has vignetting, but nothing a flat frame couldn't deal with, so I flat calibrated it and went from there. I left the ITF filter in line, but it's not needed, as I have a full aperture Aires D-ERF on front of this C8 Edge. So more testing to do there. Transmission was pretty decent (2.5ms with 0 gain).
C8_PSTMod_09112019.jpg
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C8_PSTMod2_09112019.jpg
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C8_PSTMod3_09112019.jpg
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PST_StraightThrough_5mmBF_C8Edge_DERF_ASI290MM_Transmission_09112019.jpg
PST_StraightThrough_5mmBF_C8Edge_DERF_ASI290MM_Transmission_09112019.jpg (79.96 KiB) Viewed 213 times
Image

Still more tests to do.

I think I need a larger blocking filter ideally for the C8 and the ASI290MM as I had to crop edges significantly as it was odd there.

Very best,

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Re: PST, how to replace that black box?

Post by MalVeauX » Wed Sep 11, 2019 6:52 pm

I did some more testing visually to make sure the scope was still useful. Straight through is perfect for imaging. For visual though, its still ideal to have a diagonal and a hat/cover. So I wanted to figure in a diagonal when needed.

I found that if I remove the 50mm 2" extension and insert a 1.25" star diagonal, I still can reach focus with the helical focuser and was using a 15mm 66* 1.25" eyepiece. Nice sharp view. So this works great for visual too, as if the black box was still doing its job, but minus that awful prism configuration.

So, the order is: PST objective & gold tube -> PST etalon -> AOK Swiss rear PST adapter -> M36 to 2" adapter (for the helical focuser) -> M36 1.25" helical focuser -> 1.25" nose with ITF threaded into it -> M28 to M33 adapter -> PST eyepiece cup with 5mm blocking filter -> eyepiece

So, 50mm extension inline and it's in imaging mode for both full disc and inserted into larger OTAs.
Without the 50mm extension inline, its in visual mode for standard use. And it will be ready for a SM40II double stack module.
And it's binoviewer friendly (though I don't trust that helical with a big set of heavy binos).

PST_diagonal_visual_09112019.jpg
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Re: PST, how to replace that black box?

Post by Astrophil » Thu Sep 12, 2019 2:41 am

Hey Marty,
That's a good looking mod, robust and quite versatile. Images turned out well as proof.
Either I missed something or I just don't understand. How did you attach the ITF to the 1.25 nose and was the m28 to m33 a custom adapter?

Phil

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Re: PST, how to replace that black box?

Post by marktownley » Thu Sep 12, 2019 5:16 am

You've done a great job there Marty, nice engineering solution.
Image
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Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

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Re: PST, how to replace that black box?

Post by MalVeauX » Thu Sep 12, 2019 10:50 am

Astrophil wrote:
Thu Sep 12, 2019 2:41 am
Hey Marty,
That's a good looking mod, robust and quite versatile. Images turned out well as proof.
Either I missed something or I just don't understand. How did you attach the ITF to the 1.25 nose and was the m28 to m33 a custom adapter?

Phil
Hey Phil,

The ITF threads into an eyepiece nose (1.25"), which is M28 I think? It has a little trouble initially threading, but if you file down the initial few threads it goes right in smooth after that. I have it separate from the eyecup holder. The cyccup holder has the blocking filter and is M33. So I use a M33 to M28 adapter to step it down to typical 1.25" stuff. I'll get some pictures of it all this weekend.

++++++++++++++++++++

Here's the ITF threaded into a 1.25" nose:
PST_adpated_BF_ITF.jpg
PST_adpated_BF_ITF.jpg (116.33 KiB) Viewed 133 times
Very best,
Last edited by MalVeauX on Sat Sep 14, 2019 2:51 pm, edited 1 time in total.

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Re: PST, how to replace that black box?

Post by Merlin66 » Fri Sep 13, 2019 6:14 am

Marty,
As you're still using the PST 5mm blocking/sort filter why change the ITF? I would have thought the original built in ITF would have done the job??
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Re: PST, how to replace that black box?

Post by MalVeauX » Sat Sep 14, 2019 1:36 am

Merlin66 wrote:
Fri Sep 13, 2019 6:14 am
Marty,
As you're still using the PST 5mm blocking/sort filter why change the ITF? I would have thought the original built in ITF would have done the job??
The original one I had, the ITF was part of the element (red lens) and the eyecup didn't have an ITF in it. The new one has a blue element and an ITF filter was added in that chamber. I have the two scopes and harvested parts, as the etalon that came with the newer PST has a decontacted etalon (at least I think?). My understanding was that the ITF was needed before the blocking filter with the blue element PST lens. But if that's not needed at all, I'll happily remove it.

+++++++++++++
+++++++++++++

On another note, speaking of PST mods. I'm wondering, if I take this into a 60mm F10 scope, I can get a solarmax 60mm ii module and use an adapter to thread it the new scope (like my ED80 stopped down to 60mm, producing F10) and it would effectively be a good 60mm double stack right? In this situation, does the front etalon have an ERF that would allow me to then also remove the ITF filter all together?

Are there any situations i can remove the ITF filter in a single stack use without a front mounted ERF?

Very best,

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Re: PST, how to replace that black box?

Post by Merlin66 » Sat Sep 14, 2019 2:06 am

Marty,
Belt and braces....gives some added safety.
You can never be sure of the capabilities of the ERF - some are better than others.
Don’t take the risk.
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Re: PST, how to replace that black box?

Post by MalVeauX » Sat Sep 14, 2019 2:35 am

Merlin66 wrote:
Sat Sep 14, 2019 2:06 am
Marty,
Belt and braces....gives some added safety.
You can never be sure of the capabilities of the ERF - some are better than others.
Don’t take the risk.
Strictly for imaging purposes for context, would you still use the ITF with a Solarmax 60 II module stacked in front of a PST etalon in a 60mm F10 scope with a blocking filter?

Also, what do you think of doing a SM 60 II etalon on an ED80 with a PST etalon mod inserted into its focuser? Worth while? I've never seen these types of etalons mixed or talked about so not sure if it's something that wouldn't work well or not matched well. I figured, the SM 40 II mixes with a PST etalon, so if I scale the PST etalon up to 60mm F10 with a scope and then put a SM 60 II etalon on the front of it, it's a double stack 60mm at F10 and should be ok, but I'm not sure.

Very best,

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Re: PST, how to replace that black box?

Post by Merlin66 » Sat Sep 14, 2019 4:39 am

Marty,
I use a SM60 on an ED80 with a PST etalon as a double stack.
I also use a BF10 diagonal....so effectively an ERF up front and a second in the Coronado BF.
No issues, no drama.
Using the PST etalon and SM60 is not to much different from adding a front etalon to a SolarMax II.
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Re: PST, how to replace that black box?

Post by MalVeauX » Sat Sep 14, 2019 1:49 pm

Merlin66 wrote:
Sat Sep 14, 2019 4:39 am
Marty,
I use a SM60 on an ED80 with a PST etalon as a double stack.
I also use a BF10 diagonal....so effectively an ERF up front and a second in the Coronado BF.
No issues, no drama.
Using the PST etalon and SM60 is not to much different from adding a front etalon to a SolarMax II.
Excellent to know, I think I will go this direction, rather than a SM40II so that I can have better resolution and the scope can be used to do more wavelengths, being a versatile modular system. Thanks!

Very best,

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Re: PST, how to replace that black box?

Post by MalVeauX » Sat Sep 14, 2019 8:17 pm

Merlin66 wrote:
Sat Sep 14, 2019 4:39 am
Marty,
I use a SM60 on an ED80 with a PST etalon as a double stack.
I also use a BF10 diagonal....so effectively an ERF up front and a second in the Coronado BF.
No issues, no drama.
Using the PST etalon and SM60 is not to much different from adding a front etalon to a SolarMax II.
I sent you an email regarding this configuration. :)

Very best,

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Re: PST, how to replace that black box?

Post by Astrophil » Sat Sep 14, 2019 8:38 pm

Thanks Marty,
I will give it a try if I can souce an adapter (m33 to m28.5). Do you remember where you got yours?

Phil

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Re: PST, how to replace that black box?

Post by MalVeauX » Sat Sep 14, 2019 8:47 pm

Astrophil wrote:
Sat Sep 14, 2019 8:38 pm
Thanks Marty,
I will give it a try if I can souce an adapter (m33 to m28.5). Do you remember where you got yours?

Phil
Hey Phil,

https://www.ebay.com/itm/143365782389

That's the one I got.

With a little work, it threaded into a typical 1.25" eyepiece nose. It lets me step down the eyecup and blocking filter, regardless of the ITF, to work in standard equipment.

That M33 is the same threading found in typical cheap 1.25" star diagonals. So if you didn't want to even bother with this adapter, just get a cheap old celestron 1.25" star diagonal and the eyecup stalk with the ITF & blocking filter, straight off the black box of a PST, will thread right to the diagonal and you can just use it like that too. Still eliminates the black box. I just went the extra step to remove all extra glass for imaging purposes. For visual, I insert the diagonal again as seen above.

And if anyone cares, here's the cheap 2" to M36 adapter that comes with a helical focuser (same thing found on any typical guidescope package by the way, its decent for light loads):

https://www.amazon.com/gp/product/B07HR ... UTF8&psc=1

+++++++++++++++++++++
+++++++++++++++++++++

So far, the brightness/transmission is higher, significantly so, than when it was stock. That internal prism was doing something. I'm not sure if each surface robbed transmission or what. I think it's a pentaprism if I recall. But maybe each surface soaks up a little transmission. Either way, before, I was at 10ms. Now I'm at 0.6ms with a straight through configuration and the same blocking filter, same ITF, etc. Visually its nice and bright. I just used it and could see plainly proms nicely that were feint when I compared to what's on GONG.

Very best,

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Re: PST, how to replace that black box?

Post by Astrophil » Sun Sep 15, 2019 3:40 pm

Thanks again Marty. Adapter ordered, should be here next month. Good luck with your mod.

Phil

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Re: PST, how to replace that black box?

Post by MalVeauX » Sun Sep 15, 2019 7:11 pm

Lovely little visual setup without the black box, so much sharper than before.
PST_NoBlackBox_Visual_09152019.jpg
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Very best,

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Re: PST, how to replace that black box?

Post by MalVeauX » Tue Sep 17, 2019 7:28 pm

Update:

I got all my bits and bobs together and was able to do some proper testing today.

I measured my ED80 and C6R's focus points so that I could see the overall distances to get to the magical -200mm in focus for the PST collimating lens. Turns out, with my focusers, all I needed was 1.25" roughly into the tube, and no space into the tube on my C6R (it was previously chopped for binoviewer use). So I only needed the AOK swiss adapter for the distance, and brought the collimating lens out to the tip, which kept me from having to chop 60mm or so off my OTA of the ED80 which is unmodified. The PST module I built came to focus nicely. Worked great. I stopped the ED80 down to 52mm with its internal stock cap making it around F11 or near that. Once I get a SM60 module on there it will be F10 exactly. But the test worked. I then tested with the C6R and it came to focus nicely, the resolution and detail was great! Visually both were very satisfying with good contrast. I could make out surface spicules and the limb proms no problem, was quite nice and bright. I didn't need a big expensive D-ERF either. I used an internal 50mm Baader IR CCD-R red imaging filter as an ERF and it worked great. I can insert this module into my ED80 for full disc, C6R (stopped down to 120mm F10) for high res visual and imaging, or my C8 Edge for high res imaging no problem without having to change much. Quite nice! No chopping of my OTAs. Works in all the instruments.

My next step is to get a 10mm blocking filter, got one on the way, found it used.
After that, if things look good, I will get an adapter from PreciseParts and a SM60II DS etalon to allow for full disc DS visual and imaging on the ED80.
Then... I'm done with HA and it's on to Cak...

Here's the module, completed as of now.

Image


I extended the front collimating lens out away from the PST etalon with the AOK Swiss front PST adapter. It was about 1.25 ish inches, so it was just right. I threaded the stock PST collimating lens and its internal holding disc into the M48 threads. I used a gender reversal adapter to then give it female threads. I then used a 2" spacer that is about 0.5" to give it more room and with female threads which allowed me to then thread the Baader 2" Red CCD-IR imaging filter on there, which acts as the primary D-ERF. This D-ERF internally can handle a 150mm aperture refractor no problem, as I've done this in the past with HA and CaK with this very C6R. No need for larger D-ERF nor up front with this module in 6" or less instruments (refractors only at this point).

Currently the ITF and stock 5mm blocking filter are still in line in the rear with the AOK swiss rear adapter followed by a 2" to M36 helical focuser and a M33 to M28 adapter to step down the PST eyecup with its stock BF and all that to use. Straight through. No prism. No black box. Currently this module is a stand alone that can be inserted into any of my OTAs and used vsually or for imaging without having to change much and I don't have to chop up an OTA to get it to work. Universal and modular.

Test 1

The first test was to remove the PST golden tube and 40mm objective and replace it wth another OTA. In this case, the venerable ED80, and in doing so, without having to cut the OTA. This is an ED80 with a GSO dual speed focuser. To get it to F10 (or longer) I just used the stock lens shade internal cap which is about 52mm in aperture so its around F11ish give or take. Good enough. I measured the focus point and it was about 1.25" into the focuser. The module is already set for this. Inserted it. Helical focuser allowed fine focus. It achieved focus no problem for visual and imaging. Visually it was great, good contrast, bright, full disc image with a 15mm eyepiece. Imaging, with the ASi290MM, I had to do a mosaic to do full disc, but was still good for this initial test. Can't wait to double stack it.

Image

Image


Here's a full disc mosaic made with the above ED80 + PST modular setup with an ASI290MM under poor seeing with the stock 5mm blocking filter:

Image

Test 2

The next test was then to insert this modular PST kit into a C6R, 150mm F8 achromatic refractor with its stock lens shade internal cap removed which stops the scope down to 120mm F10 which makes it perfect for PST mod use. It again came to focus no problem, and provided a wonderful visual view and was great for imaging. This OTA was cut previously for binoviewer use, but if I had to extend it, it would have been fine as I have extensions.

Image

Image


Here's a limb shot with the 120mm F10 (C6R stopped down) and the PST module kit above. The internal 50mm D-ERF (baader red imaging CCD-IR filter) worked great and handled all the heat with the module. No costly front mounted D-ERF needed here.

Image


This scope will double as my CaK scope when I get my next filter ready for 393.4nm with 6" capability on the aperture. I will primarily use this when seeing is poor and there are good proms.

++++++++++++++++++++++++

Next up with be an adapter and SM60II DS etalon to add to my ED80 for visual & imaging in HA.
Then, I will explore a CaK lunt module (1200 probably) to go from there.

Very best,

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