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 » 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.
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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.
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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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Re: Planning my first PST mod and need some help

Post by solarchatted » Sun Jul 21, 2019 10:44 am

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
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Re: Planning my first PST mod and need some help

Post by marktownley » Sun Jul 21, 2019 11:01 am

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 » Sun Jul 21, 2019 1:37 pm

This is my latest PST-SCT v2 - it is better, unfortunately no good weather today!
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PST_FocuserMod_v2.jpg
PST_FocuserMod_v2.jpg (100.64 KiB) Viewed 45 times
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sun Jul 21, 2019 1:44 pm

[/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 » Sun Jul 21, 2019 3:26 pm

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 » Mon Jul 22, 2019 9:07 am

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 » Mon Jul 22, 2019 2:21 pm

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 !!

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Re: Planning my first PST mod and need some help

Post by solarchatted » Mon Jul 22, 2019 3:11 pm

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 » 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?
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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies » 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.
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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