Planning my first PST mod and need some help

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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Re: Planning my first PST mod and need some help

Post by Merlin66 » Wed Jul 10, 2019 7:17 pm

As well as the above important comment from Mark, remember you don’t need a focuser in front of the PST etalon. Once the etalon is correctly positioned at the -200mm in front of the prime focus it should not be moved.
Any focusing behind the etalon to accommodate the eyepiece/ camera can be achieved with a spacer and a simple helical focuser - I use a BORG helical with good success.
(I also use a full aperture Baader DERF on my 100mm PST mod)
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sat Jul 13, 2019 2:00 pm

Starry Jack wrote:
Wed Jul 10, 2019 4:45 pm
What make is your AR152?
The original Explorer Scientific - not the other versions that usually have a different focuser attachment - if I am not wrong.
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sat Jul 13, 2019 2:03 pm

marktownley wrote:
Wed Jul 10, 2019 7:00 pm
solarchatted wrote:
Wed Jul 10, 2019 3:48 pm
Meade 4000 RED #25
Whhhhooooaaaaaaa!!!! DANGEROUS! This is absorptive filter, not dielectric. Stop using it, and don't use the PST mod until you have proper filtration / ERFs. This filter WILL crack and given you are using visually worries more.
I checked and it does not heat up much, it is slightly warm and I tend to put the cap on every time it is not used.

But I did understand your concerns, I already stopped using it this way - at least I got a grasp of what is going on.

... I thought the only difference between Baader RED + IR filter was simply like a Meade 4000 RED + IR/UV filter [which I have] ...
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sat Jul 13, 2019 2:14 pm

Merlin66 wrote:
Wed Jul 10, 2019 7:17 pm
As well as the above important comment from Mark, remember you don’t need a focuser in front of the PST etalon. Once the etalon is correctly positioned at the -200mm in front of the prime focus it should not be moved.
Any focusing behind the etalon to accommodate the eyepiece/ camera can be achieved with a spacer and a simple helical focuser - I use a BORG helical with good success.
(I also use a full aperture Baader DERF on my 100mm PST mod)

OK, got it.

I am thinking to actually get a M48 2" extension or stepped extension [in parts 5+5+5 etc.] and extend the front of the Etalon by screwing bits in front of AOK Swiss Front adapter and screw the PST Etalon FRONT lens in it and push it down the AR152 Focuser until I reach best focus/position I can.

I think this is the best way in my case. :bow

I will not need to modify AR152 + Etalon Tuner is accessible.

I could see I was nearly there by simply push fit the Etalon at end of Focuser tube.

After I get the extension, I only need a good DERF 100mm [pffft expensive I know but probably the most important part - safety and good filtering.

If possible, tomorrow I will also try the Etalon [in front of the focuser] ' without both lenses ' + a 2x kind of shorty Barlow I have - just to see if that could work too.
Obviously the least lenses you have the better the image [semi-educated guess!].

... I have just unscrewed the front Etalon lens ... easy peasy ... and will prepare it with 2x Barlow - hopefully tomorrow morning or late afternoon today I can try it.
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Re: Planning my first PST mod and need some help

Post by marktownley » Sat Jul 13, 2019 2:59 pm

solarchatted wrote:
Sat Jul 13, 2019 2:03 pm
... I thought the only difference between Baader RED + IR filter was simply like a Meade 4000 RED + IR/UV filter [which I have] ...
No, totally different beasts. The way the 4000 filter works is by absorbing energy, regardless of what configuration is used it will absorb energy and at some point crack. It also has a transmission of something like 25% at target (656nm) wavelength. It might be good for looking at Mars but solar is a whole different thing.
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Re: Planning my first PST mod and need some help

Post by marktownley » Sat Jul 13, 2019 3:02 pm

solarchatted wrote:
Sat Jul 13, 2019 2:14 pm
If possible, tomorrow I will also try the Etalon [in front of the focuser] ' without both lenses ' + a 2x kind of shorty Barlow I have - just to see if that could work too.
No it won't work. Don't waste your time. Many have been here with the same thought.
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Re: Planning my first PST mod and need some help

Post by Merlin66 » Sat Jul 13, 2019 4:27 pm

The most successful and probably easiest PST mods are where the donor OTA is adapted (focuser removed and OTA cut) to correctly position the PST etalon assembly at the design -200mm inside the prime focus.
Many other options are fraught with problems and difficulties.
Keep it simple, and safe.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
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Re: Planning my first PST mod and need some help

Post by marktownley » Sat Jul 13, 2019 7:41 pm

Merlin66 wrote:
Sat Jul 13, 2019 4:27 pm
Keep it simple, and safe.
Sage advice from Ken
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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies » Sat Jul 13, 2019 9:28 pm

Hi,

DO NOT use absorbtive colour filters as ERFs AFTER an objective as they absorb heat. They are only safe mounted in front of an objective.
Dielectric filters are safer after an objective as they reflect most of the energy they are not designed to let through.
An external dielectric Baader D-ERF or a Baader internal ERF using 35nm 2" or 1.25" filters which use the same dielectric technology on clear glass will work the same. The coatings will absorb the same amount of energy, say 6%, of the input energy. Intensity does not matter, as long as the filter does not melt. So the SAME amount of noise as heat will be present in the SAME solid angle. How the heat is dissipated would make a difference. It would be interesting to see videos of the two types of filter in the same telescope to see the seeing difference. And identically processed stacked images of the same length videos. Would the internal ERF pick out less good frames? Would there be a significant difference in the processed final image? And is there a different external seeing level each works at? If you do not experience very good seeing where you are an internal ERF may do.

You say you are stopping the 152mm down to 100mm to get F10.

A 1.25" 35nm Baader filter would be enough as an internal ERF. I have used one on a 110mm Vixen VMC110 which with obstruction is equivalent. For visual I use a Beloptik 1.25" KG3 with UV-IR coating on the eyepiece for complete safety.
You can use a 2" Baader 35nm up to 6" as Astrograph says. (Daystar used just a 2" UV-IR on a 10" SC at an astro fair for several days with a Quark. Filters creaked a bit it is said.)

You can put the two PST lenses in 1.25" Celestron Moon filter holders. They must be Celestron or similar looking plastic ones to be American 25.4mm (1") glass filter size and the same size as the PST etalon lenses.

I have made my PST etalon into a Quark 'Combo' Prominence by putting a tilted Omega 40nm filter in place of the front collimator lens. This is equivalent to the Andover filter in the front of the Combo, which is a soft filter by the way so degrades easily.
I may put the Beloptik in the place of the Re-focusser lens to act as a safe dust filter for the back of the etalon.

This means I can use the PST 'Combat' in F30 mode as it is or suspend the Moon filter mounted Collimator lens in front and the Re-focusser behind in F10 collimation mode.

I have found some Blue Fireball adapters.
One is a T2 male to female pass through mounting with a 1.25" filter female thread within it.
The second is a M48 Male with a 1.25" filter female thread within it. Shame they do not do a pass through M48.

You can use the front AOK Swiss PST adapter as you have to mount the Collimation lens forward enough to reach the 200mm position.
The PST adator will fit in the telescope focusser and be locked in place.
Use a M48 to T2 adapter on the front of that. Add T2 extensions till with the T2 pass through and the Celestron 1.25" Moon filter mounted Collimator lens is 200mm infront of the telescopes original focus. Careful measuring to engineering standards.
I used a T2 to M48 adapter and then 2" extension rings to position a 2" UV-IR filter where it is nearly fully illuminated to reject 50%+ of the incoming light. As a dielectric filter just a few % is absorbed and it will be 'cold' as Astrograph reports like a 35nm Baader filter. The Omega 40nm blocks ALL IR and has less reflections than the Baader. As I still have several CM of focus tube in front of the 2" UV-IR I added a 48mm to 43mm step down filter ring, Black2 painted, to block reflections off the focus tube.
I have only done a quick Stage 1 Mod bodge with the front mounted Collimator, so I know I am on the re-focusser focal plane, so far but looks OK, need to do some measurements next.

This will then just be as the original PST with the Collimating lens 200mm inside the objective focus. You will not have to go 200mm from the PST front as you can use what back focus the telescope has as well. The most back-focus you have the better as the singlet Collimator has some divergence after it.

I have the rear AOK Swiss PST adapter which accepts a 2" barrel or extension tube. The Celestron 1.25" Moon filter mounted Re-focussing lens can be put into the Blue Fireball 48mm to 1.25" adapter screwed into the front of a 48mm extension tube or diagonal, where it will just be after the PST etalon.
All you need is a low profile focusser after the PST re-focusser lens to focus eyepieces or CCDs on the re-focussing lens focal plane.

No need for a lathe.


agenaastro.com/blue-fireball-t-t2-male-m28-5-female-thread-adapter-t-10.html

agenaastro.com/blue-fireball-m48-male-m28-5-female-adapter-m-01.html

Andrew.

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Re: Planning my first PST mod and need some help

Post by solarchatted » Sun Jul 14, 2019 2:33 pm

AndiesHandyHandies wrote:
Sat Jul 13, 2019 9:28 pm
Hi,

DO NOT use absorbtive colour filters as ERFs AFTER an objective as they absorb heat. They are only safe mounted in front of an objective.
Dielectric filters are safer after an objective as they reflect most of the energy they are not designed to let through...
agenaastro.com/blue-fireball-m48-male-m28-5-female-adapter-m-01.html

Andrew.
Wow, what an informative post.

Do you have some images to actually see something of the above statements?

I hate it when I am half-knowing what I am doing.
Yes, marktownley I totally understand that - the Meade is a standard absorbing filter = danger, while Baader Red + IR is a dielectric = reflecting - same as in Electronics [my 'used to be' field] which actually is= deflecting.

Thank you
M

ps if you have the time, I do not wish to be imposing at all.
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sun Jul 14, 2019 2:43 pm

Well, what an informative and helpful forum.
You are really great guys.

So much work for this and I am back thinking that my easiest bet is a good Donor scope then, like the afore-mentioned Bresser Messier AR-90/900 OTA [far less expensive] or Bresser Messier AR-102/1000 Hex-Focus [2" focuser better for AOK Swiss adaptor] Optical Tube Assemblies.

Better a second hand one, I am very ' not liking ' to cut a tube, not the cutting, I just do not like to ruin a decent telescope, but it seems more likely I need to do that!

Pffft - back to the drawing board again - thinking time! I have so many things to do and find little time to tinker with Solar - I just wish I had a telescope done by now - ready to be taken out and enjoyed...
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sun Jul 14, 2019 2:48 pm

One thing I am not sure [regarding donor scopes].
If I get a F10 and cut it, do I still use the Etalon unit with AOK adaptors + original PST eyepiece holder as I did or not? See previous image

I am guessing all I need is to set the Etalon unit [with its lenses] ~200mm in-focus - which I guess it is not equal to 200mm cut [!] but I will have to check with a piece of paper where donor telescope focus is - i.e when it catches fire !!! and fit Etalon 200mm in that respect.

... by the way, when I fit the Etalon ' complete ' inside end of focuser - it was pretty decent - only problem I could not tune it and I also finally focused onto the surface - 178M was about 0.9ms or less - I think!
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Re: Planning my first PST mod and need some help

Post by Merlin66 » Sun Jul 14, 2019 5:06 pm

The front AOK adaptor is just a means of mounting the PST etalon to the donor scope.
The rear adaptor will need addition spacers to bring the the final focus to a position 200mm behind the PST etalon assembly.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Planning my first PST mod and need some help

Post by solarchatted » Mon Jul 15, 2019 11:52 am

Merlin66 wrote:
Sun Jul 14, 2019 5:06 pm
The front AOK adaptor is just a means of mounting the PST etalon to the donor scope.
The rear adaptor will need addition spacers to bring the the final focus to a position 200mm behind the PST etalon assembly.
OK, thanks.

In the meantime -after wasting 3 hours trying to find the PST gold tube - [it was in AOK box!], I have re-fit the SCT mod back on.

At least I have a SAFE 40mm Solar Telescope, better than the original PST.

This time with better and tight adaptors and will try and fine-tune the 200mm distance.
Getting that PST black box off is the best thing ever - it feels like having a 40mm Lunt now!
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