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 marktownley »

Here's an animation I made a few years ago that illustrates how I thought the PST etalon tilts...

Notice the wedge shaped etalon as per Dave Gs email.

Imageetalon-animation by Mark Townley, on Flickr


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

Post by AndiesHandyHandies »

Hi

I doubt its ecomomic to make high quality wedges like that.

The fact there were two feet on the bottom of the orange foam ring points to a simple tipping method.

Cheers. Andrew.


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

Post by Merlin66 »

If the spacers were squeezed during tuning the effective gap would be reduced and the CWL would move towards the red wing.
This doesn’t happen.
Tuning of the PST moves from the red wing to the blue wing. The effective gap must therefore be increasing.
This can be caused by tilt or distortion.
It has be confirmed by designer that it is based on distortion tuning.
Why not just accept what the designer says????
The feet on the orange ring were to balance the distorting forces and give a better outcome.


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

Post by Merlin66 »

Looking at the suggested animation, the effective gap would reduce during tuning.
This doesn’t happen.


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

Post by Merlin66 »

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.


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

Post by marktownley »

Merlin66 wrote: Mon Sep 20, 2021 10:34 pm Looking at the suggested animation, the effective gap would reduce during tuning.
This doesn’t happen.
It was only my 'surmising' 8 years ago now, just throwing it back in for new comers who may have not seen it, :)


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

Post by AndiesHandyHandies »

Rusted wrote: Mon Sep 20, 2021 4:22 pm An internal etalon tilter could be made using a suitable tube and two sets of spaced, radial screws.
A central O-ring could provide a fulcrum to avoid moving too far from the optical axis.
Much just like "proper" telescope finder rings. I don't know why it hasn't occurred to me before now. I was fixated on tilter plates.

An alternative would be one set of three radial screws and a compliant ring at a suitable distance.
A standard O-ring seems obvious. Much like the awful "Skywatcher" finder brackets, but much better designed.

A third alternative might be one, or two, eccentrically bored rings. To achieve tilt by independent rotation.

You'll have to do the math for the spacing. To ensure a suitable degree of tilt. Assuming the desired tilt angle is known. ;)
Hi

Fran Hourigan who was an optical designer at Wise Optics in the UK gave me a tip on adjusters which was to use 4 instead of 3. Its steadier and easier to intuitavely adjust. As metal is ductile it take up small strains, which also damp out vibrations. He made me a lovely 14" F4 on 1" plate glass for my society.

I have a 16" Dobsonian. I put 5 wind down bolts with tommy bars on the base board, so I could compare 4 feet to 3 feet. With the tommy bars I could roughly torque the feet up to bear a similar weight. And the base board will bend a bit. When moving the OTA about there was less tipping and it was steadier using 4 feet. I also had nylons rollers on plain brass bearings made to use instead of teflon pads which just wore out. Similar to HC2 focusser. Thes reduces sticktion and the differential across the wheel in diameter provides the friction. Now I can with the focusser easily push the OTA at 45 deg to both axis.

You could copy the HC2 design for your nested rotaing rings? Just move and they self lock. You have movement in x-y then.

Cheers. Andrew.


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

Post by Rusted »

I have been advocating four legged "tripods" for years.
True tripods are only good for stools on cobbled floors.
A four legged pier is deformable enough to allow rigid support without rock.
The radius of support for four feet is vast compared to a tripod.
So the tipping [hinge] line between any two feet [of four] is a huge improvement in safety and stability.
Having five feet is even better. Because it approximates even more closely to a circle. Many office chairs have five feet.
Now what was the question again? :D

tripod v quad pier tipping lines rsz 400.jpg
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Re: Coronado PST MOD2 Black RING in the middle of sun!

Post by AndiesHandyHandies »

Hi Rusted

When you have sorted out a 'trick' etalon tilter this is what I would do.

Assemble the set up with no glass in it and with a tilter. Put a Cheshire or suitable stop in the focusser. Auto-collimate the set up so the focusser is centred on the optical axis. Does not matter then if lens is off and we are only using a small field. I use a Xmas card with a hole puched in and a 1/4" thick cross on one side and stand 20 feet in front use the objective as an optical lever.

Then the etalon is on centre and you can make it orthogonal to the optical axis to start with by auto-collimating the reflection off the front.

Cheers. Andrew.


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

Post by AndiesHandyHandies »

Hi

Out of interest I did this search

https://www.google.com/search?q=pst+eta ... CA0&uact=5

Not many results and this may be the first thread to mention the orange foam feet or spacers meaning it must be tilt tuned.

Cheers. Andrew.


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

Post by AndiesHandyHandies »

Hi

Also talk of manually tuning the Orange foam ring is 'marketing urban myth', like widefield Televues being quality assured at F4 to impy they are coma correcting for Newtonians, to make you think its not just been thrown together.

Can a time and motion expert say how long it would take to make the etalon part up?

Cheers. Andrew.


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

Post by AndiesHandyHandies »

Hi

Tuning methods for a Fabry-Perot etalon are

1. Tilting - PST

2. Heating the mica spacer - Quark

3. Changing the refractive index of the air between the plates by increasing its pressure - Lunt

4. Patented RichView tuning which uses novel spacing technology and actuators to then compress the etalon and so the spacers. Coronada 90mm DS.

Cheers. Andrew.


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

Post by AndiesHandyHandies »

Hi

I have discovered via Bob that the early PSTs were tilt tuned and the later ones compression tuned.

Is there a way of telling? Serial no or change from yellow to blue coating on the front lens? Or the tilt ones have the orange foam?

Cheers. Andrew.


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

Post by Merlin66 »

Andrew, I do not believe that the information given by a senior and well respected Lunt engineer can be called an “Urban myth”.
If Bob has some evidence of PST tilt tuning, he should put it forward.
Until then my money is on Brian’s explanation.


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

Post by Merlin66 »

I have been involved in modding PST’s since 2007 and I have never come across an example which did not have the orange ring.


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

Post by Bob Yoesle »

If Bob has some evidence of PST tilt tuning, he should put it forward.
Hi Ken,

What I actually said was that "some early PST's may have been tilt-tuned." Emphasis added. I have no evidence of this tilting methodology, it is just read from posts in past amateur forums. David G. and Valery D. frequently state this was (and is) the PST tuning method:
I have taken a number of PST apart and recontacted the Etalons. The tuning mechnanism is that the Etalon is sitting against a foam ring and as the foam is compressed the Etalon tilts to tune it. It is that simple You can see the Etalon tilt by a number of degrees when you look down into the scope thru the objective . The Etalons plates are about 1/2" thick with Quartz spacers so the force needed to change the shape would be very high. The foam that Etalon sets against would have to full compressed first before any pressure would be applied to the Etalon, with a force need to change the spacing of the plates. The patent may states one thing but mechanism is tilt tuning. - Dave
On the other hand we have Spectral Joe, a physicist/engineer, and solar observer:
I don't know where the persistent belief that the PST etalon is tilt tuned comes from. The relevant patents, US 7,054,518 B2 and US 7,149,377 B2, make it clear that the etalon is tuned by compressing the spacers, the foam ring is to make the compression force symmetrical. Dismantling a PST etalon confirms this, it's built exactly as the patents show. People find it hard to believe that the spacers can be compressed, but on the spatial scale (sub-micron) involved it works just fine. You might convince yourself that they patented one thing and built another, but take one apart and see. Joe
If the spacers were squeezed during tuning the effective gap would be reduced and the CWL would move towards the red wing.
With regard to the effect of compression, it appears to me that compression and decreased etalon gap spacing would decrease the CWL:

λp = 2 n t cos θ

etalon parameteres.jpg
etalon parameteres.jpg (22.64 KiB) Viewed 3597 times

n = gap refractive index
t = gap thickness
θ = angle of incidence (tilt)

Therefore I infer from simple dimensional analysis:

1. As refractive index of the gap increases, the wavelength will increase (shift red-ward) - air pressure tuning;
2. As the gap thickness decreases, the wavelength will decrease (shift blue-ward) - "Richview" tuning;
3. As the tilt angle increases, the cosine decreases, and the wavelength decreases (shift blue-ward) - tilt tuning.

It appears from the Richview SM90II etalon I have examined that they (like most tilt-tuned etalons) have a native high CWL, and applying a compressive force to the center of the etalon (i.e. etalon gap narrows) brings the center on-band. This appears to comport with the above dimensional analysis whereby the CWL would be blue-shifted.

From what I recently observed with the LS35 etalon using a Hydrogen spectrum tube and applying compression around the periphery of the etalon face - thereby assumed to compress the spacers - the etalon also went from having a high CWL to a lower CWL with the compression applied at the periphery.

The quote you posted from Brian states with regard to the compression "It is not compressing the feet at all it is deforming the plates around the feet... The compression itself is not capable of enough force to compress the feet." I am not of want to contradict Brian, but I'm having a hard time understanding how "deforming the plates around the feet" would work in the way it appears to in my limited experiences. I have found no patent describing this deformation. There is only the patent describing compression of the spacers themselves. Then again Brian sure knows his stuff, and I'm not anything other than a curious amateur trying to understand these devices as best I can.

PS - I do note that Brian states the PST uses a Teflon ring to apply pressure to the PST etalon face, which would apparently be the bearing surface to interface with the rest of the etalon assembly in order to provide axial compression pressure.


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

Post by Merlin66 »

Bob,
I think part of your logic is wrong.
As the effective gap increases (i.e, due to tilt etc.) the CWL moves to the blue.
The Richview tuning decreases the gap and moves the CWL to the red.
I use a double stack of SM60 filters; the rear is tilt tuned (T-max) and the front one with Richview tuning and can demonstrate the above with the spectroscope.


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

Post by AndiesHandyHandies »

Hi

So if all the PSTs have the orange foam ring then they should all be tilt tuned.

If Marks video showing two little feet on one side of the orange ring is right then why is there a need to trim the foam?

Cheers. Andrew.


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

Post by Rusted »

My own, fuzzy logic suggests that the PTFE/Teflon O-ring forces alignment on the PST etalon.
The etalon element cannot tilt out of alignment because the O-ring is so hard.

The orange rubber ring ensures resistance and compliance but cannot, of itself, apply any tilt.
The reference axis for the etalon must always be orthogonal [perpendicular] to the Teflon O-ring's [three point] contact surface.

Which further suggests that if tilt is desired then the O-ring's groove must be machined at a slight tilt.
Which might be deliberately achieved with an eccentric work holder in a CNC lathe.
Or, far more likely, accidentally by typically poor [random] CNC machining using [typically] unskilled, machine minding, labour.
The coarse "tuning" thread is another possible means of applying random tilt. Accidentally or otherwise.

Note that the inner etalon housing and etalon element rotates.
Providing tilt, on demand, if the etalon's housing has tilt machined in.
Which [to the cynical] is a possible form of tuning.

Managed by changes [clocking?] at the factory under a suitable H-a test beam.
The complete randomness of the machining is overcome by optical testing [rotating] to get the etalon on band.
The multiple holes in the inner ring scream GUILTY in this respect!
If precision machining was employed then only one or three tuning holes are needed.

The PST etalon is tuned [somewhat haphazardly] because it must be. Simply to have a saleable product.
It certainly explains the [known] wide variation in PST H-alpha image quality.
"Tuning" the PST etalon is no more than production repair [i.e. fixing] of whatever the machining throws up completely randomly.
PST quality is a lottery. Like all lotteries, the many losers pay the winner. With a nice, fat profit to the lottery holder.

Any tilt I deliberately apply is external to the etalon element and applied to its inner metal housing.
All and repeatedly, in a desperate attempt to spread the inadequate sweet spot ring in my own set-up.
If I can overcome the sweet spot problem with my clumsy, tilt and turn efforts then I can achieve quite reasonable images.
Given the right seeing conditions.

I have added images to show the effect of tilting the PST etalon and "clocking" the Lunt BF against the PST etalon.

22.09.2021 11.28 1.25x 2x gpcs.jpg
22.09.2021 11.28 1.25x 2x gpcs.jpg (148.68 KiB) Viewed 3569 times
22.09.2021 14.33 1.25x 2x gpcs noise 4 ap 24.jpg
22.09.2021 14.33 1.25x 2x gpcs noise 4 ap 24.jpg (147.24 KiB) Viewed 3569 times


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

Post by Bob Yoesle »

As the effective gap increases (i.e, due to tilt etc.) the CWL moves to the blue.
The Richview tuning decreases the gap and moves the CWL to the red.
I use a double stack of SM60 filters; the rear is tilt tuned (T-max) and the front one with Richview tuning and can demonstrate the above with the spectroscope.
Hi Ken,

This does not make sense to me.

1. An air-spaced etalon is an etalon which follows the same laws of physics as a mica etalon, and with mica etalons, the etalon is tuned via heating, which increases the etalon gap via thermal expansion, which thereby increases the CWL. DayStar Whitepaper pg 13:
A Fabry‐Pérot etalon changes peak transmission wavelength with changing distance between the reflective sides. This can occur by a change in temperature through thermal expansion of the mica wafer. In order to maintain the center wavelength (CWL) of the Fabry‐Pérot etalon in conditions of varying environmental temperature, a consideration for tuning must be made. An increase in temperature causes an increase of the CWL of transmission peaks. The etalon varies 1.0Å per 17.0 °F (9.4 °C). The Quantum uses a temperature regulated oven to effect tuning and control of wavelength.
So why would an air-spaced etalon perform the exact opposite (decreased gap = increased CWL)?

2. I have used Hydrogen spectrum tubes to observe the change in etalon fringes as compression is applied to the center of a Richview etalon (and the periphery of a LS35), and the CWL is lowered by observing the central donut becoming smaller with compression. Christian has also evaluated a Richview etalon, and notes the native CWL is high, and the etalon is tuned by applying Richview compression. If decreasing the gap via compression increased the CWL, the etalon would never come on-band, and indeed would go farther off-band.

The issue of tilt seeming to increasing the gap distance and resulting in blue-shifting the CWL is indeed a factor which originally had me confused. However, I was assured that tilt blue-shifted the etalon per the etalon equation cosine theta figure, not the presumed increased distance traversed through the gap. Therefore the equation is absolutely correct, and not my original "common sense" interpretation and conclusions. I have yet to have a conversation with anyone fluent enough in etalon physics to resolve the seeming contradiction. It seems paradoxical to me still, but that's the reality of etalon physics.
Last edited by Bob Yoesle on Wed Sep 22, 2021 5:04 pm, edited 1 time in total.


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

Post by AndiesHandyHandies »

Merlin66 wrote: Wed Sep 22, 2021 5:33 am Bob,
I think part of your logic is wrong.
As the effective gap increases (i.e, due to tilt etc.) the CWL moves to the blue.
The Richview tuning decreases the gap and moves the CWL to the red.
I use a double stack of SM60 filters; the rear is tilt tuned (T-max) and the front one with Richview tuning and can demonstrate the above with the spectroscope.
Hi Ken,

When you took the PST etalons apart were the orange rings all like Marks with two little feet on one side. Were they part of a moulding or stuck on?

Cheers. Andrew.


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

Post by AndiesHandyHandies »

AndiesHandyHandies wrote: Wed Sep 22, 2021 4:12 pm
Merlin66 wrote: Wed Sep 22, 2021 5:33 am Bob,
I think part of your logic is wrong.
As the effective gap increases (i.e, due to tilt etc.) the CWL moves to the blue.
The Richview tuning decreases the gap and moves the CWL to the red.
I use a double stack of SM60 filters; the rear is tilt tuned (T-max) and the front one with Richview tuning and can demonstrate the above with the spectroscope.
Hi Ken,

When you took the PST etalons apart were the orange rings all like Marks with two little feet on one side. Were they part of a moulding or stuck on?

Cheers. Andrew.
Hi Ken,

If we have a tuned etalon at a certain wavelength where a whole no of wavelengths fit in then if the space increases slightly for whole wavelengths to fit in the wavelength has to be smaller and one more wave fit in. So thats why it shifts to the blue. And vice-versa. Where the wavelength increases and one less wave fits in.

Counter intuative.

Cheers. Andrew.


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

Post by AndiesHandyHandies »

Hi

This continues for a bit and then we get to a point where a longer wavelength starts to fit in again and we get back to the original wavelength which is how the combs are created.

We did an etalon experiment at Birmingham. We had one mirror on a micrometer and 3 light sources. Two were given. We had to move the mirror a certain amount, the same for each wavelength and count the no of fringes there were for each. We were given a clue as to what it was. Everyone else spent 2 weeks with a mechanical calculator going through guesses until by co-incidence they found the right answer by co-incidences.

I was the first under-graduate to ask to use their brand new IBM360, with 1MB of free memory as it was 18months late. I got given a Fortran 70 manual which is in my sons loft.

So when I ran the program I could do lots of calculations. It was interesting there were lots of co-incidences within an iterference pattern envelope. The centre loop was biggest and just one co-incidence at the centre with the highest point on the graph. I think this means you need to auto-collimate the front of the etalon first to be nearest to the brightest peak in the comb which I would think will be when its at exactly 90deg to the optical axis.

I ran a beuraue service after that and saved people 2 weeks in the lab. Unfortunately the lab supervisor was the second year chief tutor so when I complained about my supervision groups useless tutor I did not get much change.

Cheers. Andrew.


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

Post by Merlin66 »

Andrew,
From memory, there were some orange rings with one block and some with none. I can't remember seeing a ring with two feet.


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

Post by AndiesHandyHandies »

Merlin66 wrote: Thu Sep 23, 2021 5:22 am Andrew,
From memory, there were some orange rings with one block and some with none. I can't remember seeing a ring with two feet.
Hi Ken,

Thanks for the feedback.

So that seems to indicate the etalons are built and fergled in some way as said.

I assume the pads are stuck on then.

RodAstro says the PST is well built as it needs to be. The prism holder is machine out of a solid block of alloy for instance.
He says my PST is from the first year of production, his mate bought it.

When Mark took his apart the etalon just dropped out. Not mechanically indexed in any way and 'rattling' about in the holder. So that implies where it sits is not critcal for its functioning. And you can see the orange foam has sunk with age and pressure.

RodAstro said Stuart eventually had to have a solid alloy tube machined out for his triple stack as things screwed together was too floppy.

The patent which comes up associated with the PST when I search, Bob linked to, clearly states it uses compression of the etalon.

As Rusted says you would expect the foam to push the bare etalon back onto the teflon ring, so when the sweet spot wobbles about as you tune it must be play in the adjuster thread. So one assumes the pads are put in to take out play in the thread??? Valery says the reflections off his PST etalon move about as its tuned.

Your experiment with the DS shows that the tilted etalon CWL goes towards the blue and the Richfield compression one towards the red.

Can you do the same experiment on a PST? If its made to the patent the CWL should move to the red.

Thanks. Andrew.


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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 106 times
Coronado 60 review.pdf
(571.38 KiB) Downloaded 96 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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