Coronado PST MOD2 Black RING in the middle of sun!

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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

OK, I'll retest a PST etalon at the next opportunity.
In the meantime some reading matter on etalon tuning.
http://www.astrosurf.com/viladrich/astr ... P-Coro.htm
etalon_tilt_pressure_v4.xls
(293.5 KiB) Downloaded 14 times
Coronado 60 review.pdf
(571.38 KiB) Downloaded 8 times


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi

I have thought it would be neat to colour code doppler shifted images and 3D layer them in Photoshop.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

Astroart can now present a GIF file which shows that animation.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi Ken,

Thanks for the reading matter.

This shows why you need to be on the centre comb I think.

https://www.researchgate.net/figure/Fil ... _282972240

Cheers. Andrew.
Last edited by AndiesHandyHandies on Sat Sep 25, 2021 9:15 am, edited 1 time in total.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi

RodAstro observed the M class flare yesterday with his Quark and was concerned as it looked nearly white and bright if he was safe.

I asked here if anyone had done a spectrum of a Quark but no answer. Concern is long IR really. Whilst you are testing the PST would it be possible to do a full spectrum on a bare quark? I could not find any info on the web before.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

Andrew,
If you send me a Quark, I’d be happy to test it.
I don’t have one, and there are none in use locally.
We’re in lockdown and can only travel 5km.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

OK, Limited opportunity but did collect some data:
1.The limit of rotation for the PST adjuster is approx 160 degrees
2.Looking from the back (black box side) Extreme RHS tuning is well into the blue wing. Extreme LHS is just beyond Ha CWL into the red wing. The Ha CWL is approx LHS minus 10-15 degree.
3. The orange ring is compressed as the tuner is rotated towards the LHS i.e. towards the red wing.
The PST orange ring I tested has only one "foot".


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Merlin66 wrote: Fri Sep 24, 2021 10:24 pm Andrew,
If you send me a Quark, I’d be happy to test it.
I don’t have one, and there are none in use locally.
We’re in lockdown and can only travel 5km.
Hi

Fair enough.

That is a bit limiting.

Thanks. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Merlin66 wrote: Tue Sep 21, 2021 1:24 am OK, here's a copy of the original email:
Hi Ken,
The PST uses compression tuning. Probably the worst way imaginable to tune an etalon. The Teflon ring in the chamber is the main point of pressure. The silicone ring is designed to smash the etalon until it comes into tune. Since it never compresses evenly the silicone ring is trimmed and cut so that it applies pressure as evenly as possible. This can only be done while applying pressure with the rotational compression ring and trimming parts of the silicone while looking through the chamber at a hydrogen spectrum light. It is not compressing the feet at all it is deforming the plates around the feet. That is why the silicone is trimmed to even out etalon while it is crushed. The compression itself is not capable of enough force to compress the feet. And compression the feet since they are fuse silica as well would in fact crack crush or powder the feet to a point of loss of contact. Thus destroying the etalon.
Hope that helps.
Hi Ken

"The PST uses compression tuning."

later

" The compression itself is not capable of enough force to compress the feet. And compression the feet since they are fuse silica as well would in fact crack crush or powder the feet to a point of loss of contact. Thus destroying the etalon. "

How is this possible?
"Since it never compresses evenly the silicone ring is trimmed and cut so that it applies pressure as evenly as possible. This can only be done while applying pressure with the rotational compression ring and trimming parts of the silicone while looking through the chamber at a hydrogen spectrum light."
Not compatible with the various no of feet seen from zero to two. Surely look through the etalon and then stick a foot on based on that.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Merlin66 wrote: Sat Sep 25, 2021 1:37 am OK, Limited opportunity but did collect some data:
1.The limit of rotation for the PST adjuster is approx 160 degrees
2.Looking from the back (black box side) Extreme RHS tuning is well into the blue wing. Extreme LHS is just beyond Ha CWL into the red wing. The Ha CWL is approx LHS minus 10-15 degree.
3. The orange ring is compressed as the tuner is rotated towards the LHS i.e. towards the red wing.
The PST orange ring I tested has only one "foot".
Hi Ken

So if its going towards the blue turning it from the LHS where its red its tilting. Valery reports the reflections off the etalon moving as its tuned. And I have seen pictures of the reflection at the front of a PST doing just that.

So the orange ring with or without feet is holding the etalon tight on the teflon ring at the LHS. As it is tuned towads the RHS the pressure reduces and the uneveness in the foam, aided by a foot/feet where needed, allows the etalon to tilt, off the teflon ring OR just a bit or reduction in the pressure allows the teflon to rebound where the pressure is less, and it is working by compression but of the teflon, which needs less force I presume than compressing spacers. Its not enough to bend the etalon plates or there would be banding issues.

"When you have eliminated the impossible you are only left with the possible".

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi Ken

Cogitating in the bath.

Or its relying on machining tolerance in the adjuster thread? Which would be in a random orientation and depend on how the etalon housing thread seats. So testing has to be done in situ for tuning and the optional feet.

If you take an etalon apart and remove the orange ring it needs to be indexed so its put back in the same place. Has anyone taken the ring out and heated it gently to get it to re-bound?

Try wrapping a bit of PTFE round the adjuster thread. Does it change the rotation needed to tune? There seems quiet a bit of leeway. Is it then more sensitive? Does the sweetspot wobble about less as you tune?

Would lapping the adjuster threads improve tuning then? Danger of upsetting the orientation I suppose.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by marktownley »

AndiesHandyHandies wrote: Sat Sep 25, 2021 10:53 am Try wrapping a bit of PTFE round the adjuster thread. Does it change the rotation needed to tune? There seems quiet a bit of leeway. Is it then more sensitive? Does the sweetspot wobble about less as you tune?
I've done this, there is less movement of the sweet spot.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi

Actually is the centre of the teflon ring smaller than the centre of the orange ring? If so then the simplest explanation is the highest/stiffest part of the Orange ring is applying tilt by it pivoting on its side of the teflon ring. The etalon glass is stiff enough not to be distorted by the force required. Feet have to added if the variations in the stiffness of the orange ring are not enough, or maybe to account for manufacuring tolerances.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi Ken,

When the adjuster is on the LHS the orange ring is under most pressure and the etalon is pressed against the teflon ring. Mark confirmed that putting teflon tape on the adjuster ring the sweet spot moved about less, so I do not think its slop in the adjuster causing any tilt. When it pressed against the teflon ring the etalon should be at right angles to the optical axis, which is needed to be near the centre comb. CV says it needs to be within a degree orthogonal and half a degree is needed for tuning, one degree between combs.

When the pressure on the teflon ring mounted on the adjuster ring decreases then the differential pressure from the orange ring comes into play, accentuated by the extra stiffness, foot, or feet for 'the special one'.

There are two possible mechanisms:

1. Decrompression on one side of the teflon ring allows it to expand, opposite where a stiffer spot or the added feet are, and so the etalon tilts. So its de-compression tuned.

2. The feet or stiffer spot keep pushing that side of the etalon and it tilts down on the other side with the teflon ring under the feet acting as a fulcrum where the pressure is now lower. My best bet at the moment.

In either case the direction the etalon tips in should be orthoganol to the foot in your case, useful you have one with a foot.

How can we tell which one it is? Cogitating with an icepack on my back.

We need to set the PST on tune and then rotate the ajuster ring back to the LHS. We need to integrate the force needed to compress the orange ring. When its tuned back the integrated force is acting on the teflon ring on one side as the other side de-compresses. Stick a bar into one of the tuner holes and press it with a set of scales. I did that on my 16" dobsoinian with the roller bearings on the bottom and normal teflon bearings and plastic tube on the side. Luckily the stiction was 500g and the friction was 300g on both axis, which is why its easy to push at 45deg. We then need CV to calculate if the teflon modulus of elasticity and the net force will produce the right tilt.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

Merlin66 wrote: Sun Sep 26, 2021 6:35 am Andrew,
As the pressure reduces on the orange ring, the CWL tends towards the blue.
When there’s no pressure on the orange ring (and we assume also on the etalon) it is sitting well into the blue wing.
What mechanism would move the CWL under increasing pressure towards the red????


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

Just posted a correction.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

AndiesHandyHandies wrote: Sat Sep 25, 2021 9:22 am
Merlin66 wrote: Tue Sep 21, 2021 1:24 am OK, here's a copy of the original email:
Hi Ken,
The PST uses compression tuning. Probably the worst way imaginable to tune an etalon. The Teflon ring in the chamber is the main point of pressure. The silicone ring is designed to smash the etalon until it comes into tune. Since it never compresses evenly the silicone ring is trimmed and cut so that it applies pressure as evenly as possible. This can only be done while applying pressure with the rotational compression ring and trimming parts of the silicone while looking through the chamber at a hydrogen spectrum light. It is not compressing the feet at all it is deforming the plates around the feet. That is why the silicone is trimmed to even out etalon while it is crushed. The compression itself is not capable of enough force to compress the feet. And compression the feet since they are fuse silica as well would in fact crack crush or powder the feet to a point of loss of contact. Thus destroying the etalon.
Hope that helps.
Hi Ken

"The PST uses compression tuning."

later

" The compression itself is not capable of enough force to compress the feet. And compression the feet since they are fuse silica as well would in fact crack crush or powder the feet to a point of loss of contact. Thus destroying the etalon. "

How is this possible?
"Since it never compresses evenly the silicone ring is trimmed and cut so that it applies pressure as evenly as possible. This can only be done while applying pressure with the rotational compression ring and trimming parts of the silicone while looking through the chamber at a hydrogen spectrum light."
Not compatible with the various no of feet seen from zero to two. Surely look through the etalon and then stick a foot on based on that.

Cheers. Andrew.
Hi Ken,

Have you seen signs of the orange ring being butchered with a knife?

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Merlin66 wrote: Mon Sep 27, 2021 4:42 am
Merlin66 wrote: Sun Sep 26, 2021 6:35 am Andrew,
As the pressure reduces on the orange ring, the CWL tends towards the blue.
When there’s no pressure on the orange ring (and we assume also on the etalon) it is sitting well into the blue wing.
What mechanism would move the CWL under increasing pressure towards the red????
Hi Ken,

Whats the correction?

"As the pressure reduces on the orange ring, the CWL tends towards the blue."
You said with the adjuster ring turned towards the LHS from the back that the foam was fully compressed. I assume that despite the 'feet' all the foam is compressed and the etalon is pressed all round onto the teflon ring. If the compression in the teflon ring is causing the tilt it should be tilted towards the 'foot' a bit, but not enough to be more than half a degree from orthogonal to be on the central band as it then should tilt away from the foot.

"When there’s no pressure on the orange ring (and we assume also on the etalon) it is sitting well into the blue wing."
When is there no pressure on the orange ring then? When the adjuster ring is rotated to the RHS? How can you tell there is no pressure? How can you tell if the 'foot' is not still pressing the etalon onto the teflon ring?

"What mechanism would move the CWL under increasing pressure towards the red????"
The etalon is not being tuned by compression of the mica feet I presume. As its clearly being tilted as the adjuster ring is rotated to the RHS. And the CWL is moving towards the blue meaning it must be tilt tuned.
As you tune towards the RHS the reflection off the front of the etalon should move away from the 'foot'.
When you start to move towards the RHS from the LHS the back pressure from the orange foam decreases. Because there is more pressure on one side, in the plain foam ring or aided by foot or feet (foot), as the adjuster is rotated one side of the etalon opposite the 'foot' experiences less pressure. At some point that can reduce enough for the differential compression across the teflon ring to tilt tune the etalon, but with pressure still on the other side. Thats the differential pressure we need to try and measure to see what the 'differential rebound' of the teflon ring on that side would be and if thats enough across that diameter of the teflon ring from the 'foot' to tilt tune the etalon.
If its not enough the tilting from the orange ring being bigger? than the teflon ring can also tilt it in the same direction away from the 'foot'.

As there are two possible ways the same tilt can be imparted it hard to tell which is predominant or whther both are in play.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

Andrew,
""
How can you tell if the 'foot' is not still pressing the etalon onto the teflon ring?
""
You can go to the extreme and see the orange ring "go loose" within the assembly. As you continue to rotate the tuner the etalon appears to turn but the orange ring remains stationary.
I don't see any evidence of tilting. The rear of the etalon appears in complete contact with the white teflon ring at all times.
If the etalon tilted would it not show in the contact with the teflon ring?


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi Ken,

"You can go to the extreme and see the orange ring "go loose" within the assembly. As you continue to rotate the tuner the etalon appears to turn but the orange ring remains stationary."
Do you mean turning it to the far RHS? If the orange ring de-contacts with the etalon what holds the etalon against the teflon ring? In Marks diss-assembly video the etalon is loose in the cell and covered in clear grease. Clearence round the edge of the etalon. A depression in the orange ring a bit off centre.

"I don't see any evidence of tilting. The rear of the etalon appears in complete contact with the white teflon ring at all times.
If the etalon tilted would it not show in the contact with the teflon ring?"
If compression in the teflon ring is doing the tilting it can be in contact all the time. If the etalon spacers were being compressed to tune the CWL would shift to the red? This would mean the teflon is much more compressible than the mica feet?

If each etalon is checked and for some a foot or feet ( or bits carved off the foam? ), are added in order for it tune properly then they must be applying a off-axis additional force for a reason?

I assume the teflon ring is attached to the underside of the tuning ring. As it appears to be in the video.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi

I have read the patent and the text talks about using pressure actuators to pressure tune an etalon!
And also speculates on springs or other elastic materials for the spacers.

The drawings do look like a PST though, which we know has no pressure actuators.

Ken has shown the CWL of the PST shifts towards the blue as its tuned which is the Hallmark of tilt tuning.

https://patents.google.com/patent/US7054518

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by Merlin66 »

Andrew,
I've never seen an orange ring "notched out" only the added foot.
"""If compression in the teflon ring is doing the tilting.."" I don't believe the teflon ring is being compressed/ distorted. I think it's just a mechanism to apply uniform pressure on the etalon.

"" the CWL of the PST shifts towards the blue as its tuned""" Yeah, but............I equally could have said the CWL moves towards the red wing as it's tuned. What's the definition of "tuning"
In the "rest" position - no movement of the tuner, and minimal/ non pressure on the etalon, sitting on the RH stop the CWL is in the blue wing. Then "tuning" does take you to the red wing.......


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

AndiesHandyHandies wrote: Mon Sep 27, 2021 10:08 pm Hi

I have read the patent and the text talks about using pressure actuators to pressure tune an etalon!
And also speculates on springs or other elastic materials for the spacers.

The drawings do look like a PST though, which we know has no pressure actuators.

Ken has shown the CWL of the PST shifts towards the blue as its tuned which is the Hallmark of tilt tuning.

https://patents.google.com/patent/US7054518

Cheers. Andrew.
Hi

Looks like the PST drawings were used to describe old ways with a noddy wedge added for non uniform pressure. And a child drew the last diagram with springy bits. Flying a flag to try and get priority on 'novel use' for solar filters for mainstream technology elsewhere.

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Merlin66 wrote: Mon Sep 27, 2021 10:49 pm Andrew,
I've never seen an orange ring "notched out" only the added foot.
"""If compression in the teflon ring is doing the tilting.."" I don't believe the teflon ring is being compressed/ distorted. I think it's just a mechanism to apply uniform pressure on the etalon.

"" the CWL of the PST shifts towards the blue as its tuned""" Yeah, but............I equally could have said the CWL moves towards the red wing as it's tuned. What's the definition of "tuning"
In the "rest" position - no movement of the tuner, and minimal/ non pressure on the etalon, sitting on the RH stop the CWL is in the blue wing. Then "tuning" does take you to the red wing.......
Hi Ken,

Before the tuning starts the etalon needs to be within 1 degree of orthogonal. I tune my PST etalon afresh by turning to the LHS and then towards the RHS and the small sweet spot soon appears and as I keep moving becomes an expanding circle.

The modulus of elasticity for glass is 50 and for PTFE is 0.5, in modern units, so the PTFE is 100 times more compressible.

At the LHS the orange foam is firmly pressing the etalon on to the PTFE ring then onto the adjuster body, which should be whithin 1 degree of the etalon housing axis I would hope. On the far RHS if there is no contact between the orange ring then the etalon can be anywhere, as its not a sliding fit and loose in the housing.

If the manual testing indicates a foot needs adding then a larger off axis force is needed.

Where is the refection off the front of the PST when on the LHS? And how does it move as you start turning the tuner to the right?

Cheers. Andrew.


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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi

As you tune the PST from the LHS past the sweet spot the spot expands into a ring.

I would expect the tilt and compression tuned etalons have the rings go the opposite way?

So in the DS Ken tested the he should see that difference, and he knows the back etalon is tilt tuned and the front etalon has Richview compression tuning.

Cheers. Andrew.
Last edited by AndiesHandyHandies on Tue Sep 28, 2021 9:40 pm, edited 2 times in total.


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