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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 solarchatted » Thu Jul 25, 2019 4:00 pm

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 » Fri Jul 26, 2019 6:22 am

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 » 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.
"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 » Fri Jul 26, 2019 2:06 pm

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 » Fri Jul 26, 2019 2:18 pm

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 894 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 » 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!
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sat Jul 27, 2019 8:56 am

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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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies » Sun Jul 28, 2019 11:45 am

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 » Sun Jul 28, 2019 3:01 pm

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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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies » Sun Jul 28, 2019 7:19 pm

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 » Mon Jul 29, 2019 8:58 am

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 » Mon Jul 29, 2019 1:22 pm

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 » Mon Jul 29, 2019 10:10 pm

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 » Thu Aug 01, 2019 8:25 am

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 » Wed Aug 07, 2019 1:33 pm

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 781 times
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Re: Planning my first PST mod and need some help

Post by solarchatted » Wed Aug 07, 2019 1:50 pm

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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Re: Planning my first PST mod and need some help

Post by marktownley » Wed Aug 07, 2019 2:10 pm

Are the lenses back to front?
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sat Aug 10, 2019 2:54 pm

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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Re: Planning my first PST mod and need some help

Post by solarchatted » Sat Aug 10, 2019 4:31 pm

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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Re: Planning my first PST mod and need some help

Post by solarchatted » Sun Aug 18, 2019 4:20 pm

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 681 times
AR90-AR102 Focuser mod
AR90-AR102 Focuser mod
AR90-900AR102focuserMod.jpg (181.06 KiB) Viewed 681 times
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Re: Planning my first PST mod and need some help

Post by marktownley » Tue Aug 20, 2019 6:31 am

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 » Wed Aug 21, 2019 10:23 am

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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Re: Planning my first PST mod and need some help

Post by AndiesHandyHandies » Wed Aug 21, 2019 3:52 pm

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 » Sat Aug 24, 2019 11:19 am

Will drill holes, good idea of course and get hot currents off the chamber in between lenses and D-ERF - thanks!
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Re: Planning my first PST mod and need some help

Post by solarchatted » Sat Aug 24, 2019 11:26 am

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.
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