Planning my first PST mod and need some help

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Re: Planning my first PST mod and need some help

Post by Merlin66 »

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 »

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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Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

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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https://astronomo.space/my-images/the-sun/
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Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

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.


SolarChatted
https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by marktownley »

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 »

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 »

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.


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Re: Planning my first PST mod and need some help

Post by marktownley »

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 »

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 »

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.


SolarChatted
https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

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...


SolarChatted
https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

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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https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by Merlin66 »

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.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

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!


SolarChatted
https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

Hi
I am back to something that works ... I keep it on this thread as it has been gathering info to help others too.

This morning I set-up for re-testing my SCT mod and it works great - actually better [etalon seems better after I removed lenses once and put them back without doing anything - weird!] and it is a bit different and I now have ~200mm from centre of Etalon to tip of 2x Barlow [fit onto the camera or Seben Zoom for visual or full disk + camera ... it works - tested a long time ago!].

I also inserted a 2" IR/UV before the PST eyepiece holder - behind the Etalon and also added a that Meade series 4000 #25 RED filter and is getting nice and sharp visually [they are protected by the reflective front PST lens anyway].

Then I fit my Altair 178M and focused just 3mm inwards from visual focus - not bad.

Then I added my 2.2X telephoto lens in front of PST front lens [as in sweiller test] and I easily focused visually by just 7mm back, now trying to focus camera but it has clouded up - I never get to end a session of tests ever with our wonderful weather!

My next attempt should be next Wednesday [day off] around 12-14:00 should be clear after a possible hard-shower [!] - but I will leave telescope up today and hope for a 10 minutes clear enough to be able to focus and possibly take an image ... or rain!

I do have a couple of questions about the cheap Bresser AR-90L-1200 [F/13.3] - yes it has a 1.25" focuser, but I do not see what impact on the VERY bright Sun would do. - https://www.bresseruk.com/review/product/list/id/6223/

1. Do you think Bresser AR-90L-1200 is a decent choice for a PST mod?

2. How much should I cut Bresser AR-90L-1200 to get focus ?
I am asking as I see many just cut around 100-120mm and not the whole 200mm

3. I might get the 75mm ERF [cost less] and inserted internally at correct distance [I have to either calculate or play with a couple of strings or tape measure to find the right position.
Doing the insert is easy, my only problem is what to use as ERF holder, being actually 80mm [75mm ERF opening] ans tube is 90mm, although may be less inwards.
Any ideas? I know the 90mm is easier [being actually 100mm or 105mm wide and make a cap] but its price is ridiculous high [for my small pockets]
I might try to find a kind of nylon strip to wrap around and attach to inserter - it must be thin.

4. ERF type Baader 75mm or Lunt 75mm - the price is the difference for me, but usually Baader is the best one. IS it worth the price difference?


Thank you for all your help, I am getting there and understanding a bit more now. :bow
Mauro


SolarChatted
https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by marktownley »

solarchatted wrote: Sun Jul 21, 2019 10:44 am
I also inserted a 2" IR/UV before the PST eyepiece holder - behind the Etalon and also added a that Meade series 4000 #25 RED filter and is getting nice and sharp visually [they are protected by the reflective front PST lens anyway].


I do have a couple of questions about the cheap Bresser AR-90L-1200 [F/13.3] - yes it has a 1.25" focuser, but I do not see what impact on the VERY bright Sun would do. - https://www.bresseruk.com/review/product/list/id/6223/

1. Do you think Bresser AR-90L-1200 is a decent choice for a PST mod?

2. How much should I cut Bresser AR-90L-1200 to get focus ?
I am asking as I see many just cut around 100-120mm and not the whole 200mm

3. I might get the 75mm ERF [cost less] and inserted internally at correct distance [I have to either calculate or play with a couple of strings or tape measure to find the right position.
Doing the insert is easy, my only problem is what to use as ERF holder, being actually 80mm [75mm ERF opening] ans tube is 90mm, although may be less inwards.
Any ideas? I know the 90mm is easier [being actually 100mm or 105mm wide and make a cap] but its price is ridiculous high [for my small pockets]
I might try to find a kind of nylon strip to wrap around and attach to inserter - it must be thin.

4. ERF type Baader 75mm or Lunt 75mm - the price is the difference for me, but usually Baader is the best one. IS it worth the price difference?
The use of the Meade 4000 filter still concerns me. It's an absorptive filter, it will crack at some point!

In the world of solar you pays your money and takes your choice. A decent focuser is key in a PST mod, the mod kit hanging off the back of that 1.25" focuser is likely that it will sag, this tilts the etalon and will cause it to go off band.

You need a f10 scope for a PST mod to work ideally, the 90/1200 is f13.3, it will only complicate things and result in sub optimal performance.

In terms of sub aperture ERFs wrapping the perimeter of the ERF in electrical tape to male up to the correct diameter for an interference fit in the tube would work. A couple of self tapping screws immediately either side of it would act as retainers.

The Lunt ERF is much thinner than the Baader, just means wavefront error is likely to be higher.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

This is my latest PST-SCT v2 - it is better, unfortunately no good weather today!
Attachments
PST_FocuserMod_v2.jpg
PST_FocuserMod_v2.jpg (100.64 KiB) Viewed 7182 times


SolarChatted
https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

[/quote]

The use of the Meade 4000 filter still concerns me. It's an absorptive filter, it will crack at some point!


[/quote]

Thanks for the info ... and regarding the RED filter, I only meant within this mod - i.e. the PST tube is in front of it - the IR/UV + RED is fit on the 35mm extension after the etalon ... as a test and it seemed contrasting well - for the few minutes I had with this weather.

Regarding the AR90/1200 F/13.3, I always thought PST mod was F/10 upwards and not F/10 full stop.


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Re: Planning my first PST mod and need some help

Post by Merlin66 »

If the donor is faster than f10, the etalon assembly will act as an aperture stop and give an effective f10 system.
If the donor is >f10 then the beam is not affected by the etalon assembly and will still give a system >f10.
Example: an f8 say 100/800mm will become a 80/800mm system; an f12 say 100/1200mm will still be an f12, 100/1200mm system.


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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies »

Hi

Read this post about PST safety

www.diane-neisius.de/coronado_pst/index_E.html

I got an adapter from the PST front thread to M48 so I can put a 2" Baader 35nm and/or a Belpotic 2" KG3 with UV-IR blocking at the front to make the PST safe. My original PST with the ERF on the front is rusted so RodAstro wants to take the lens apart and polish off the coating so I will need the front filters then.

The problem with 4" F10 telescopes is their size. But a cheap one is good for cutting down.

Another way is to get a cheap F6 and add a Baader 1.25" 1.25x glasspath Barlow in front of the etalon. As there its effectively 200mm in front of the focal point it works as a 1.5x Barlow. F6 x 1.5 = F9. The PST will vignette it to F10. You could space the Barlow a bit further forward with extension tubes, as in my post before to get to F10. Laying out my bits I found I need a M48 to T2 adapter as the extension tubes in front of the PST are 'going the wrong way', handed because of the threads.

Andrew

I have a TS F6.7 I am going to add the Baader Barlow to to get F10. Lighter than my 127mm F7.5 for testing anyway.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

Hi
Thank all for the further info.
I have ordered a Bresser AR90/900 - let's see what happens.

I will need to find exactly how much to cut! Brrrr - no mistakes allowed here !!

Mauro


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Re: Planning my first PST mod and need some help

Post by solarchatted »

AndiesHandyHandies wrote: Mon Jul 22, 2019 9:07 am
Read this post about PST safety

www.diane-neisius.de/coronado_pst/index_E.html
Yes, I remember that article thanks for link - that was what made me use the 2" 'standard IR/UV in front of Etalon on the SCT mod I have in the meantime and added a std red filter that 'never' heated up when I tested the AR152.

I decided if I have to do a decent solar scope, better use a cheap donor one like AR90/900 and eave AR152 alone [for now anyway] I prefer not to use further lenses.

I am sure a 90mm F/10 + a 75mm right placed ERF will do a good job - I am an amateur not a scientist, although we always aim to better ourselves - we seem to never stop!

;p]

PS when I use it visually, I also add another 1.25" IR/UV filter onto my Seben 8-24mm Zoom - I wonder if we can use a mobile phone camera and a IR/UV app to generally measure danger levels!
Last edited by solarchatted on Mon Jul 22, 2019 3:19 pm, edited 1 time in total.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

Just curious, but regarding the BF10 [probably for the future], why not try and find just the 10mm BF glass and drill the PST 5mm to 10mm and replace it?

Is that possible? I mean find a BF10 - just the glass?


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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies »

Hi

The AR90 looks a good choice as available new. I never came across it when looking for a OTA.

I would first use it with the 2" UV-IR placed up the tube where its just under fully illuminated.
The dielectric filters only absorb a bit of energy in the coating. For the space telescope I used for an example a coating absorbs 6% on a mirror. Anti-reflection coatings do absorb more.

Unless you find the telescope seeing is worse than your typical atmospheric seeing at 90mm aperture then a big ERF is a luxury. Daytime seeing will be worse than nighttime. AstroRod says 40x is a popular eyepiece magnification. The eye can resolve 2 arc minutes. So 120 arc seconds / 40 = 3arc seconds which is probably typical daytime seeing.

As I said a D-ERF (external) or a ERF(internal) using the same technology will absorb the same percentage of heat, and its in the same solid angle.

Andrew.

Andrew


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Re: Planning my first PST mod and need some help

Post by solarchatted »

News!
Got the AR90/900mm F/10 Bresser Refractor - everything is plastic but the tube !
Even the focuser is plastic - I mean the whole focuser block held by 3x 8mm Parker screws - that is what you get for just around £. 100

Anyway, dismounted the original plastic focuser and I was left with ~85mm hole and a 90-100g Tuna Fish Tin just fits with 0.5mm spare ...

So, I drilled the main hole 50mm [using 2mm drill bits] then used a Rasp for Metal over the drill to shape it and reasonably forced AOK Etalon to 2" adaptor in and screwed back onto the SCT/PST focuser unit.

The Tuna Tin is sited to make Etalon 18cm inwards - I simply measured from centre of front AR90 lens to back and it just happen to be about 5mm inside the end of the tube [without its original focuser] = LUCK - finally some ...

I will have to do another Tuna Fish Tin but shorter - fit it the other way around - as it touches the Etalon and I cannot push it forward in another 2cm.

Hopefully make it 20cm exact.

I tried it for a few minutes on a ' wobbly ' camera tripod and it seemed to almost be in focus at maximum 25mm out of the SCT focuser - that conforms it needs to be 10-20mm more inward - hence the Tuna Fish Tin modification.

Tomorrow morning or until I am home for a short break [Sunday], I will try telescope properly on EQ6 - more stable - and manually move the focuser in out to see how much more I need - if needed anything.

Once I have the correct distance, I will see to make an adaptor with something sturdier.

Pity I cannot afford a 3d Printer or that would have been an easy solution.

PS still user IR/UV + RED filter - did not heat and also image seems slightly dimmer than the AR152 cut down to 100mm - better telescope lenses I guess.

These are quick tests, I do not see any danger as I have been using it for hours no cracks no t heating at all.

Then the 75mm [or less] ERF - I noticed telescope has a cut don plate to ~ 50mm at about 28.5cm from edge of tube - focuser side - therefore I might only need a 63mm the one used for SCT's - I am guessing here.

That means I can easily slide it on it and lock it with some strong thick black foam forced in - I might fit it over the lens side - if lens side comes off - I am guessing they have glued it on this model !!!

to be continued ...


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Re: Planning my first PST mod and need some help

Post by solarchatted »

AndiesHandyHandies wrote: Tue Jul 23, 2019 10:20 am Hi

The AR90 looks a good choice as available new. I never came across it when looking for a OTA.

I would first use it with the 2" UV-IR placed up the tube where its just under fully illuminated.


Andrew
I usually have 2" UV/IR fit onto the AOK adaptor ~5cm before the Etalon + RED [I know, can be dangerous] filter.

Having a had a quick look into the AR90/900 I have to say, I might only need the Baader RED IR [reflective] or a smaller less expensive ERF
Thanks as usual ... well explained.

:bow


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Re: Planning my first PST mod and need some help

Post by marktownley »

solarchatted wrote: Mon Jul 22, 2019 3:17 pm Just curious, but regarding the BF10 [probably for the future], why not try and find just the 10mm BF glass and drill the PST 5mm to 10mm and replace it?

Is that possible? I mean find a BF10 - just the glass?
The only place you will find the filter in a bf10 is in the the bf10 filter, you won't buy them separately.


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Re: Planning my first PST mod and need some help

Post by Merlin66 »

Please,please, listen to the experienced advice your are being given.
Your safety and that of others following this thread is paramount.
We do not support any unsafe modding of the PST or any other commercial solar scope.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

Merlin66 wrote: Fri Jul 26, 2019 8:24 am Please,please, listen to the experienced advice your are being given.
Your safety and that of others following this thread is paramount.
We do not support any unsafe modding of the PST or any other commercial solar scope.
Agreed.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

Next will be the ERF [maybe 2nd 3rd week of August] - probably the 75mm [80mm] Lunt and fit inside at about 28.5cm from edge of tube - focuser side.

I am getting some 80mm O-rings and already made a nylon pressed-in plate to hold the ERF in place over the internal original telescope metal plate with a 50mm hole already cut in it - pity wasting 75mm for a 50mm hole. It is almost placed 2/3 down tube [from front lens], so beam should be 2/3 smaller ~30mm - not too hot I guess... Please tell me if I am wrong!

Going back to present mod, I managed to fit PST Etalon/Eyepiece Holder + SCT unit onto end of telescope using its 3 holes and making an adaptor Mod to Telescope using a Tuna Fish Tin, that just fits in it and making a hole and snapped Tin in between Etalon and AOK adaptor. Then made 3 holes and used original 'standard' Parker screws to hold.
I might need to go in a bit more 5-15mm max to get into the 200mm exact focus from the Etalon.

I did try it this morning to see if I was correct in focusing distance and I already see a huge difference - even if it still is not exactly in correct FL.

See this image for example - I keep my images on my website anyway: https://astronomo.space/my-images/the-sun
1024 x 768
1024 x 768
SUN2019JULY2610X76SAR90.jpg (319.69 KiB) Viewed 7516 times
It is only 1024x768 from a Altair 178M

I will have to use a long ~25cm dovetail and a couple of rings I already have, as this long tube is too wobbly!

...

Just thought of it, I did make a 30cm Drain Pipe [~110mm] tube with Nylon thumbscrews a few years back and might use that as telescope bracket


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Re: Planning my first PST mod and need some help

Post by marktownley »

Heya.

I would make sure the ERF is as high up the tube as possible so it intercepts as much of the exit beam from the objective as possible. Aim more like 2/3 up the tube.

The -200mm is so important, I get you're just trying stuff but fundamentally just aim for -200mm in the first place. Just measure it!

Had a look at your website. The camera is a bad choice in it's basic form - 2.4um pixels are way too small. Use the camera in 2x2 binning, the (then) effective pixel size is much better suited and the gain in exposure time will also be on your side.

All this will help!


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Re: Planning my first PST mod and need some help

Post by solarchatted »

marktownley wrote: Fri Jul 26, 2019 6:11 pm Heya.

I would make sure the ERF is as high up the tube as possible so it intercepts as much of the exit beam from the objective as possible. Aim more like 2/3 up the tube.

The -200mm is so important, I get you're just trying stuff but fundamentally just aim for -200mm in the first place. Just measure it!

Had a look at your website. The camera is a bad choice in it's basic form - 2.4um pixels are way too small. Use the camera in 2x2 binning, the (then) effective pixel size is much better suited and the gain in exposure time will also be on your side.

All this will help!
Hi


1. The centre of the Etalon still is 15mm outwards in the tube - needs to go 15mm inwards to be at 700mm FL.
Have to find a way of doing it, without cutting tube - if possible - as 700mm FL is just 5mm inside the end of the metal tube - luckily - that is why I use that Tin just to see if it was not far off and it is not.

2. I agree with the ERF distance logic [fact!], the nearest to the lens the less currents, temperature on it and also sharpness should improve too. Problem with this cheap scope, I believe the front shield is actually glued on it - not pressed in! I also noticed is not even straight ...

I have to see if I can take it off, then take lens off ans see if there is another place inside - like the one at 28.5cm from back of tube - that would be great - just avoiding cutting tube and also trying to avoid to buy a 90/100mm to put in front as it is too expensive for me.

The beam at 28.5cm is must be 28.5mm - in fact there is a 50mm hole on that plate.
If there is one at about 30cm from front, beam should be 60mm and hole maybe 72-73mm.

I have to see, when I get time.

3. Must get or find a 25-30cm dovetail to fit my rings and make telescope less wobbly.

Yes, about the binning, I have used it a few times and you are right, of course - it becomes a 4.8µm + faster acquisitions.

Thanks for your help.


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Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies »

Hi

You can buy the Comb Blocking filters Daystar use from Andover:
FeroT wrote: ?
Tue Feb 21, 2017 6:07 pm
Andover makes the BF for Daystar Quark (656FS02-12.5), it is 12.5mm diameter and cost $157 for one piece. I have replaced it with a 25mm diameter one (656FS02-25) and use it with TV 4xPowerMate to DS the LUNT50 etalon with Quark. The specification of the filter is 656.3nm Bandpass Filter, FWHM 1nm, 12.5mm dia.

25mm is better quality someone said.

The 12.5mm would do for the 90/900 as the sun will be 9mm in diameter.

Are you going to buy a later yellow Lunt ERF?

For a 90mm a Baader 2" 35nm ( or a 7nm which reduces the wings a bit) would be perfectly safe as an ERF. Placed where its fully illuminated up the tube.

Andrew.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

When I mentioned to replace the BF within the PST original 6mm [mine is I think], I believe I read somewhere a long time ago, someone else drilling the 6mm hole to 10mm or so and replace filter.

Do you mean this Andover? https://www.andovercorp.com/
The filter is actually 171$ today.

Thanks for your help.

---

I dismounted the front of this telescope and YES :hamster: there is [as expected] another metal ring welded in.

It is at about 20cm from front lens - did not measure distance but hole diameter seems to be 79-80mm - it 'could' fit the Lunt 75mm (80mm) ERF.

I also drilled 3 more holes at focuser side and pushed Etalon 10-11mm inwards (not 15mm as I measured earlier) - it should now be bang on 700mm.

Once I see that it works decently OK, I will start to think how to make an adaptor and take the Tuna Fish Tin off it.

The thing is, the original 'plastic' focuser is 1.25" - although I could use my modified (with 3 nylon thumbscrews) Chinese 1.25" to 2" adaptor and actually cut the tube and use the plastic focuser... mmm ... :seesaw ... or could try and find a 2" clamp (diam. ~84.9mm) that fits within the telescope tube ... we will see

...


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Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies »

Hi

My link was from a couple of years ago!

Remember the Comb Filter is at an angle which you want to keep if you drill it out.
To throw reflections off axis, which you can see if you took the PST Black Box plate off.
Also the pentaprism is set at an angle for the same reason. All the photos of an original show the same offset.

Good luck.

Andrew.


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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies »

Hi

If you are getting a coloured glass ERF it will absorb 66% of the visible light, if its UV-IR coated.

A 2" Baader 35nm will only absorb 6%? of the light and reflect the rest. And pass only 10% of the visible as opposed to 33%.
Astrograph sells 6" refractors with a Baader 35nm as the ERF.

If you are concerned about the long IR the Baader passes use a Beloptic KG3 on the eyepiece as I do.

Andrew.

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Re: Planning my first PST mod and need some help

Post by marktownley »

The Andover filters are what are used in the Quarks, they won't work as blockers with other etalons.


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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies »

Hi Mark,

I forgot about the difference in the etalons.

Andrew.


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Re: Planning my first PST mod and need some help

Post by marktownley »

This may be of interest? viewtopic.php?f=11&t=26388


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Re: Planning my first PST mod and need some help

Post by solarchatted »

I recently [ after I did take those images] removed the front lenses to make sure there was a internal ring near the front and there is one and the 75mm [80mm] ERF should fit fine.

My problem is, i am not 100% sure I re-fit the front lenses correctly, even thou I did place them on a clean surface aligned!

This AR90/900 is an achromatic and I guessed the lenses being a Bi-Convex and a Flat-Concave with a spacer aligned like this - see image.

I cannot focus properly any more!

Lenses are clear - not damaged.

I re-attached original focuser and used a Zoom to focus near buildings and focus is not 100% focused - visually image is cloudy as in slightly out of focus, so I thought I might have fit them incorrectly.

I checked the lenses and they are supposedly correctly fit.

I am confused now - as mentioned I never studied Optics!

Thanks
Mauro
Attachments
BiConvex_PianoConcave.jpg
BiConvex_PianoConcave.jpg (24.49 KiB) Viewed 7403 times


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Re: Planning my first PST mod and need some help

Post by solarchatted »

I guessed I was too near!

I do not know how to calculate minimum distance for focusing, but I went outside picking something more distant and focus went better, then I picked up nearest hill - a few hundreds metres away and it does focus.

I also discovered what an amount of rubbish these lenses are!
It still not a sharp focus + surroundings of lens is defocused a bit - that is what I noticed when I tried the Sun ... the other day.

It should be OK, then - might wait for Moon to come out, although it might be too low from my point of view.


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Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by marktownley »

Are the lenses back to front?


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Re: Planning my first PST mod and need some help

Post by solarchatted »

Mine is fit like this:
https://en.wikipedia.org/wiki/File:Lens6b-en.svg

But upon checking it now, the front seems to NOT be equal on both sides!

I cannot check right now as I had to clear table, but possibly tomorrow morning.

Is it possible front lens is not convex equally on this telescope?

MAuro


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Solar Gear:
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Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

Well ...
I will test lenses properly when I get the time, the weather and the Moon or stars and also measure its focus using the AR90/900 with its own focuser from the end of the tube to edge of camera 178M - to avoid mistakes - the 178M has about 10-12mm inside to reach CMOS - not much.

Going back to the unfinished mod, I finally got a 50mm Hole-saw and re-done the Tuna Fish Tin adaptor and it finally is stable.
Waiting for weather and match it with my home-time to test again or possibly ...

... change to a better Plan:

1. shorten AR90/900 tube after I measured focus [as above] - still not absolutely sure how much [trying not to make mistakes] and use its plastic 1.25" tuner as intended!

2. get the whole SCT block which works well and it has now become a variable Focuser [ ~ 18 to 22cm ] for Etalon only

3. get another Chinese 2" to 1.25" adaptor - will order next week

4. fit it over AOK 2" Etalon adaptor - but then I will be adding about 5cm [have to measure it] ... blooming 1.25" ' plastic ' focuser !
IMPORTANT BEFORE I CUT - I need to try and find a metal 2" focuser that fits the tube and not add 5cm to the cut!
If I am not wrong it is just short of 85mm width.

This way I will have a Tube focuser + Etalon Focuser + Etalon Tuner - to hopefully get a decent focus with these cheap lenses.

Yes, I think it is certainly a better plan with what I can afford at present.

Of course I will need the D-ERF ... on order - I do not wish to blind myself or anybody else - I have become a grandad lately and in a couple of years I will show the little one the universe, starting with The Sun and The Moon!

When he gets older I might give him my ST80 and a photographic cheap tripod for himself.

Mine is a long process, because I cannot spend + need to find the time and the weather when needed + it is also is a learning process.


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Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

Hi all

Today I stepped up again.

I had the brilliant idea of using my AR102ST focuser onto the AR90-900 and replace the awful plastic 1.25" focuser with a metal properly made one and 2" - although it only has 45mm focus adjustment and I had to add 35mm extension to focus - original focuser tube is very long.
I guess the 35mm extension takes the place of a diagonal.

I thought it should fit and it did, by fitting it externally - i.e. AR90 tube inside AR102ST focuser unit.
I mean it fits exactly and I added 3x screws using its own threaded holes - just to push onto the AR90 tube - no holes, yet anyway.

Now the last 3 problems remain:

1. I must make sure I cut the ' correct amount ' off the tube! - see image of how I tested focus distance using Thousand Oaks Filter and a 25mm eyepiece - although in theory if I cut 20cm it should be OK I always can use the first AR102SX focuser to adjust Etalon to correct 7200mm inside focus and then fine focus the eyepiece or camera using the SCT focuser, then Tune Etalon and re-focus if necessary - I am a little bit scared to make a mistake in cutting on wrong length! :?

2. I will have to fit the Baader D-ERF inside [coming soon] - should not be a problem.

3. FIXED

I have fit the front unequal biconvex lens with the MORE convex part towards the spacer - I really thought it was the other way around.
It now focuses very well!


I noticed when I look into the eyepiece, I have to move my eye a bit to side to actually get rid of a unfocused halo over the edge of The Sun - after I focused it!
I do not understand this - it might be to do with the front lenses ... possibly.
I believe they are correctly re-mounted - as mentioned earlier. :? Pfffsss

Any idea on blurry edge of the Sun when focused?
I mean moving my head [i.e the eye] around I can see the edge 'is' focused - it must be to do with the lenses -I do not see what else is the matter.
I will have to find time to focus on The Moon - better than stars - but ... I am confused.
It was the same when I tried Etalon with Red filter shortly - just the same.
Attachments
AR90-AR102 + SCT focuser + PST bits
AR90-AR102 + SCT focuser + PST bits
AR90AR102andSCTfocusersPSTmod.jpg (146.24 KiB) Viewed 7303 times
AR90-AR102 Focuser mod
AR90-AR102 Focuser mod
AR90-900AR102focuserMod.jpg (181.06 KiB) Viewed 7303 times


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Solar Gear:
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Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by marktownley »

Looks like you're making some good progress there Mauro. Glad you sorted out the focus position. The extra focuser works well, just watch the weight doesn't add flexure to the system.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

I have dismounted the lenses and focuser to prepare for cutting.

The D-ERF filter fits nicely just behind the front lenses as there is a step after the step where lenses sit - so 90mm lenses and 70mm D-ERF view.

I will try that first and see what happens - if it masks too much, after I cut the tube.
It might not be today - pity The Sun is out ... or it would be dark :lol:

ADDITION - on second thought I might fit the D-ERF about 20cm more inside [from the front lens] there is another step and that should let the whole 70mm opening through.


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Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies »

Hi

If its a cheap scope you cut cut ventilating holes in the tube above the internal DERF.

With some shading baffle over for skylight.

Andrew.


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Re: Planning my first PST mod and need some help

Post by solarchatted »

Will drill holes, good idea of course and get hot currents off the chamber in between lenses and D-ERF - thanks!


SolarChatted
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https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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Re: Planning my first PST mod and need some help

Post by solarchatted »

By the way, I have finally managed to test live with The Sun still in between clouds!

It works and I must say, I should have cut it less than the 22cm I did [after I measured], while initially I wanted to cut 15.5-16cm - I was right!
I had to add about 6-7cm extension!
In other words when I calculated it I was correct 15.5-16cm, when I measured it I got it wrong!
If I feel to do it I might actually add back a 6cm cut of from the ' cut-off ' of 22cm and plate it on it to extend it then seal with silicone if needed or even epoxy [better] and get rid of extension - less warping ... if any!

I get same or better quality than PST - as in sharpness, but obviously magnified since lens is 90mm and not 40mm.

I tried imaging too, I will try to process one or two today, but I will have to stop at 2pm - we got a nice barbecue to get ready for my Father-in-law 83rd birthday - an ex-miner since he was 16 years old until the strike and closure.


SolarChatted
https://astronomo.space/my-images/the-sun/
https://www.youtube.com/@Astronomo_Space

Solar Gear:
Bresser AR90/900 + PST mod + SW Auto Focuser ...
Sometime I use Explorer Scientific AR152/988 + Used once only... Altair 2" Solar Wedge (very good indeed)
Will try and do it justice when I can with the help of various filters, Baader 1.25" Solar Continuum 10nm is one.
SW 72ED Pro - fixed 'stock faulty' focuser ... 'I think' !
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