Etalon PST problem - NEWS

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Etalon PST problem - NEWS

Post by pupak »

I disassembled two etalons from PST and the silicone pads are heavily damaged. Can it work properly with them? When I tested the etalons, I always set only part of the field of view to the band, approx. 20-30%. This seems completely useless to me and I don't understand how anyone could sell this.
Is this really damage or does it have some hidden meaning?
I am planning to make new precision silicone pads, but I would hate to make them wrong.
Thanks for every opinion.
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new silikon pad
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Last edited by pupak on Sat Feb 04, 2023 2:51 pm, edited 1 time in total.


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Re: Etalon PST problem

Post by MalVeauX »

I've seen many of these degrade over time. They're just there to hold the etalon plates "somewhere" in the chamber. The edges keep it rough collimated. The pressure on the plates tunes them. The sponges are just there to take mechanical stress from the compressing. You can replace that material with another compressible material.

Very best,


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Re: Etalon PST problem

Post by pupak »

MalVeauX wrote: Mon Jan 30, 2023 12:47 pm I've seen many of these degrade over time. They're just there to hold the etalon plates "somewhere" in the chamber. The edges keep it rough collimated. The pressure on the plates tunes them. The sponges are just there to take mechanical stress from the compressing. You can replace that material with another compressible material.

Very best,
I understand their function, but I assumed that it was desirable that the pressure be uniform around the entire circumference of the etalon, otherwise there will be an uneven displacement of the two parts of the etalon relative to each other.


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Re: Etalon PST problem

Post by MalVeauX »

pupak wrote: Mon Jan 30, 2023 1:35 pm
MalVeauX wrote: Mon Jan 30, 2023 12:47 pm I've seen many of these degrade over time. They're just there to hold the etalon plates "somewhere" in the chamber. The edges keep it rough collimated. The pressure on the plates tunes them. The sponges are just there to take mechanical stress from the compressing. You can replace that material with another compressible material.

Very best,
I understand their function, but I assumed that it was desirable that the pressure be uniform around the entire circumference of the etalon, otherwise there will be an uneven displacement of the two parts of the etalon relative to each other.
The spacer between them and optical contact between them keeps them uniform (or to whatever degree uniformity they have, few are actually uniform). The sponges just keeps them "floating" in the chamber. Any tilt from the sponge just shifts CWL bandpass. But yes, if really tilted due to this, they will be way off band (towards blue) which means you have to really tune hard towards red to get back on the CWL and likely will have bad banding.

Very best,


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Re: Etalon PST problem

Post by Valery »

Pupak,

Nothing wrong with the etalon itself. The picture you see on the solar disk is "banding".
It just due to too much tilt required to come to the Ha CWL. This given etalon require too much tilt and you can see the results of such too much tilting - sponges are damaged.

I have tested MANY telescopes PST during my quest for a very narrow PST etalon which also does not require too much tilt in the conditions (typical barometric pressure and air temperature) in my area.

With PST etalons we have absolutely the same problems as with front mounted tilt tuning etalons Lunt and Coronado.

This given etalon may work flawlessly at high altitude. The only ways out are:

1. To sell it to someone who are at high altitude.
2. To make a similar pressure tuner for this given etalon (see Bob Yoesle's invention for LS35 etalon).

Valery
Last edited by Valery on Wed Feb 01, 2023 2:19 pm, edited 1 time in total.


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Re: Etalon PST problem

Post by pupak »

Thanks for the anwers. I thought the PST etalon was pressure tuned, not pitch tuned. So does this mean that turning the tuning ring changes the tilt of the etalon in the case relative to the optical axis? If so, then the construction of the etalon is very bad, because everything points to the fact that the tuning should be pressure. Even the drawing in the standard patent indicates pressure tuning. I am somewhat confused by this.
viewtopic.php?t=27491
This thread clearly states that the PST etalon is pressure tuned, not pitch tuned. Then, however, the silicone pad, which by its stiffness determines the degree of compression of the etalon, should be homogeneous to avoid tilting.


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Re: Etalon PST problem

Post by pupak »

Although I haven't had a chance to test the etalon yet, I made an exact silicone pad. I wonder if the display quality will change.
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Re: Etalon PST problem

Post by marktownley »

Keep us updated Petr!


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Re: Etalon PST problem

Post by Bob Yoesle »

This thread clearly states that the PST etalon is pressure tuned, not pitch tuned. Then, however, the silicone pad, which by its stiffness determines the degree of compression of the etalon, should be homogeneous to avoid tilting.
Exactly.

I will love to see how well this will work - nice job!

I'm not an engineer, but I have stayed at a Holiday Inn or two ;-)

The only issue that may crop up is that the blue silicone you've used may be a bit stiffer than the orange foam rubber, and the coarse adjustment of the PST threads might make fine mechanical pressure adjustments a bit more difficult.

If I were a machinist I'd completely redesign the entire collimator/etalon/refocusing lens system to have a peripherally "silicone potted" etalon sitting on the blue silicone seat, and apply the pressure via the roller bearing/plate method, used with a finer compression thread. That would essentially eliminate any tilt and/or torque applied to the PST's etalon via its Teflon compression O ring and foam rubber seat, and give you finer control of the amount of pressure applied.

But if you really want to get serious, seal the etalon chamber and apply vacuum tuning! :geek:

Bob


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Re: Etalon PST problem

Post by pupak »

I have been thinking about vacuum tuning since the very beginning. I have my pressure controller for the LUNT etalons, and there you just need to switch the input and output of the compressor. I already have a model of the case made, but I want to test the new pad first.


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Re: Etalon PST problem

Post by marktownley »

It would be good to be able to simply drop a PST etalon into a pressure tunable body. It would be possible to 3D print two halves of body with a soft gasket on the joining face. It would just need a suitable valve. Entramce and exit Lenses would be easy to mount like this.


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Re: Etalon PST problem

Post by pupak »

marktownley wrote: Wed Feb 01, 2023 6:41 am It would be good to be able to simply drop a PST etalon into a pressure tunable body. It would be possible to 3D print two halves of body with a soft gasket on the joining face. It would just need a suitable valve. Entramce and exit Lenses would be easy to mount like this.
So far I have designed a simple duralumin housing composed of two coaxial tubes. In the inner one there is a etalon sealed with silicone and the outer one is used to fix it into the system. The vacuum inlet is via a 6 mm fitting.
There are certainly a number of other solutions. This is easy for me to make.
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Re: Etalon PST problem

Post by marktownley »

Yup, I can see how that would work.


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Re: Etalon PST problem

Post by Valery »

pupak wrote: Tue Jan 31, 2023 1:26 pm Although I haven't had a chance to test the etalon yet, I made an exact silicone pad. I wonder if the display quality will change.
Petr,

I hope you will succeed with this silicone pad. I believe it can has a commercial success.
The next can be pressure tuned LS35, LS40, LS50 and LS60 etalons. Why not?


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Re: Etalon PST problem

Post by pupak »

I'll find out if the pad works when the sun finally comes out. I'm not holding out much hope, but maybe the picture will improve enough to make the etalon usable.
I definitely have another toy to experiment with, even if it was expensive enough to only be used for playing. If that doesn't work, the next round is vacuum tuning. :)


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Re: Etalon PST problem

Post by pupak »

I also proposed an overpressure variant, which is simpler in terms of tuning and does not require a vacuum.
The space of the pressure chamber is filled with wax, and after covering both parts with silicone, the wax is removed with heat, leaving an empty space. An entrance fitting leads into it. Since almost no axial movement is required, the elasticity of the silicone ensures the transfer of pressure to the etalon. It's just an idea.
I see it as an advantage that there is no need for additional glasses to maintain overpressure.
It will still need to be refined for production.
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Re: Etalon PST problem

Post by Bob Yoesle »

Brilliant idea!

My concern would be that the uniformity, thickness, and length of the silicone for the pressure piston would have to be very uniform. If not, the piston might not compress equally around the etalon periphery. Worth trying to see what happens...


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Re: Etalon PST problem

Post by pupak »

Bob Yoesle wrote: Fri Feb 03, 2023 12:37 pm Brilliant idea!

My concern would be that the uniformity, thickness, and length of the silicone for the pressure piston would have to be very uniform. If not, the piston might not compress equally around the etalon periphery. Worth trying to see what happens...
It is enough to use silicone of hardness I., which is very flexible. Degassing in the vacuum chamber will also increase the homogeneity of the seal. Only a real test will show the truth.


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A new method of pressure tuning.

Post by pupak »

For a long time I was looking for a way to compress the etalon and keep the pressure control simple and accurate.
Finally, I thought of the electromagnetic principle, where a coil in an iron ring attracts a second iron ring through a thin spring pad, which pushes on the standard. Regulation using PWM will certainly be accurate and fine enough. I did the first test with the electromagnetic brake from the servo motor and the pressure force is regulated by the PWM controller absolutely perfectly. No gaskets, no tubing, just two wires to the coil. This is exactly what I was looking for all along. The idea is in the picture in the attachment.
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Re: Etalon PST problem - NEWS

Post by DavidG »

I'm sorry but the Etalon in a PST is a simple tilt tune mechanism and not pressure tuned by mechanical force applied to deform the Etalon. The patent is red herring about pressure tuning by applying force to the Etalon. It is not used in a PST. The end of the tuning ring is machined on a slight angle and when you turn it, it causes the Etalon to be push into the foam ring and tilt. The foam deforms in a non uniform way which also causes it to tilt. As an engineer and some one who made optics for 40 years including designing solar instruments you can not get enough force on the Etalon to tune it by deforming the plates when it is support by a foam ring. To have enough mechanical force to deform the plates work, the Etalon must be firmly held in place so any force applied is transmitted to the plates to deform them. When supported by foam all the force is transmitted to the foam and no deformation of the plates occur.
Here are two pictures that show the tilting of the Etalon to tune it. I aimed my PST at the Sun and you can see the Sunlight reflected off the Etalon on the inside of the telescope tube and when I tune it on band the reflection moves because the Etalon is tilting. It just a very simple tilt mechanism. The tilting of the Etalon is the majority of how the band width is shifted vs any caused by the pressure applied the plates. You can see it yourself by looking down the tube at Etalon as you turn the tuning ring and watch it tilt. It uses the KISS principle.

- Dave
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Re: Etalon PST problem - NEWS

Post by pupak »

DavidG wrote: Sun Feb 05, 2023 3:08 pm I'm sorry but the Etalon in a PST is a simple tilt tune mechanism and not pressure tuned by mechanical force applied to deform the Etalon. The patent is red herring about pressure tuning by applying force to the Etalon. It is not used in a PST. The end of the tuning ring is machined on a slight angle and when you turn it, it causes the Etalon to be push into the foam ring and tilt. The foam deforms in a non uniform way which also causes it to tilt. As an engineer and some one who made optics for 40 years including designing solar instruments you can not get enough force on the Etalon to tune it by deforming the plates when it is support by a foam ring. To have enough mechanical force to deform the plates work, the Etalon must be firmly held in place so any force applied is transmitted to the plates to deform them. When supported by foam all the force is transmitted to the foam and no deformation of the plates occur.
Here are two pictures that show the tilting of the Etalon to tune it. I aimed my PST at the Sun and you can see the Sunlight reflected off the Etalon on the inside of the telescope tube and when I tune it on band the reflection moves because the Etalon is tilting. It just a very simple tilt mechanism. The tilting of the Etalon is the majority of how the band width is shifted vs any caused by the pressure applied the plates. You can see it yourself by looking down the tube at Etalon as you turn the tuning ring and watch it tilt. It uses the KISS principle.

- Dave
Obviously, every person has a different opinion. :)
It's really hard to know where the truth is. The text and images of the patent allude to pressure tuning.
....................................................................
Post by Merlin66 » Mon Mar 30, 2020 11:38 pm

OK guys...here's the definitive answer on how the PST etalon is actually tuned!
After almost 15 years of guessing/ discussion/ debate etc. I managed to get a reply from my contact who has worked with assembly and testing of the PST in production....
I asked the question:

The options I think are:

1. The PST etalon tuning is achieved by tilting of the etalon
2. The PST etalon is tuned by pressure applied to the spacers in the etalon
3. The PST etalon is tuned by increasing/ decreasing the atmospheric pressure around the etalon
4. Another method????

The answer.....drum roll..... #4 another method!!!

The PST uses compression tuning. The Teflon ring in the chamber is the main point of pressure. The silicone ring ( the orange foam) 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 spacers at all, it is deforming the plates around the spacers. That is why the silicone is trimmed to even out etalon while it is crushed.

I don't think any of us figured on that answer.......
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Re: Etalon PST problem - NEWS

Post by Bob Yoesle »

It is not compressing the spacers at all, it is deforming the plates around the spacers. That is why the silicone is trimmed to even out etalon while it is crushed. Emphasis added.
As an engineer and some one who made optics for 40 years including designing solar instruments you can not get enough force on the Etalon to tune it by deforming the plates when it is support by a foam ring. To have enough mechanical force to deform the plates work, the Etalon must be firmly held in place so any force applied is transmitted to the plates to deform them. When supported by foam all the force is transmitted to the foam and no deformation of the plates occur. Emphasis added
I will have to disagree with both of these statements. I know it is difficult to believe that relatively small mechanical forces could compress a fused silica etalon spacer to the degree necessary to affect the etalon gap spacing or deform the etalon plates (I had to first see it for myself), but the dimensional changes are so small that very little force is needed, and this is exactly what "Richview" and other forms of mechanical tuning are doing in order to change the etalon gap spacing. The other methods for tuning being of course changing the etalon gap refractive index (air pressure), or tilting the etalon to change the CWL blueward. With solid etalons, temperature changes are usually used to change the etalon gap spacing and thereby change the etalon CWL.

Mechanical pressure etalon tuning was patented at Coronado by Andy and David Lunt et.al., first applied for in 2004. It was first implemented by Bill Dean at Coronado with the "high resolution" collimator based internal air spaced etalons that had CWLs just slightly above the H alpha emission. A central pin attached to the collimator lens compressed the central spacer and decreased the etalon gap and thereby decreased the overall etalon CWL to get on-band:

SM90 internal module K LeGore.jpg
SM90 internal module K LeGore.jpg (125.19 KiB) Viewed 2878 times
An early Coronado SM90 MaxScope internal "high resolution module" belonging to Kevin LeGore, which is stated to have belonged originally to David Lunt himself:

David Lunt's SM90 DS internal.jpg
David Lunt's SM90 DS internal.jpg (456.14 KiB) Viewed 2878 times

Mechanical compression as shown in the patent was later put to use in the PST where compression of the peripheral spacers accomplishes lowering the etalon CWL. If the etalon plates were deformed without compression as depicted in the diagram shown by Ken, the etalon gap would increase at the center of the etalon, and the CWL would shift higher, taking the etalon further off-band.

My postulate is that any observed tilt in the PST etalon reflects the fact that the etalon "floats" on its foam rubber seat, and the Teflon ring imparts a slight torque to the etalon possibly exacerbating the etalons lack of fixation. If tilt tuning was going to be implemented for the PST, it could have been easily and done much better via the well-established internal tilt plate methodology that had been in place for years with the Helios 1 and the original tilt-tuned BF30 blocking filters:

Helios 1 tilt plate spring sm.jpg
Helios 1 tilt plate spring sm.jpg (220.55 KiB) Viewed 2878 times

This very simple and stable screw-adjusted tilt-tuning method was later implemented for the front etalon TMAx tilt-tuners, and remains today for all the front mounted etalon systems used by Coronado Meade, Lunt, and Solarscope. This would also mean the supposed compression and hand-trimmed foam seat tilt-tuned etalon of the PST would have to be done for every PST, which would be a more labor intensive (expensive) methodology for an entry level low-priced filter system, and doesn't therefore make much sense to me.

In every air-spaced etalon I have seen, the etalon rests on a soft foam rubber support ring. In the "RIchview" SM90II etalon I had a chance to work with, it uses a central pressure pin attached to the ERF, and a threaded internal etalon base is used to rotate the ERF with its attached pin to apply increasing amount of mechanical pressure directly to central etalon spacer. Also of note in this implementation, no peripheral etalon support around the etalon plates is provided. This is essentially the PSTs compression tuning implementation, only a central pin is used instead of a peripheral Teflon ring. I am at a loss to understand why a peripheral Teflon ring is not added (hint: do a DIY) to help better balance the compressive forces applied in the SMII and SMIII etalons...

Additionally, the uncompressed etalon CWL was very high (large central fringe ring below left), and when sufficient pressure was used to get the central region on-band (below middle), the compressed central etalon spacer decreases the etalon gap in the center and deforms the etalon plate spacing resulting in the mid and peripheral zones remaining off-band high (below right), and the overall etalon band pass was over 1A:

SM90II fringes.jpg
SM90II fringes.jpg (586.36 KiB) Viewed 2878 times

No combination of tilt or mechanical pressure allowed the etalon to perform well as a single stack etalon, but it was marginally OK for a double stacking etalon. Note however, the lower etalon plate is secured with "smears" of black silicone sloppily applied to the bottom plate side, perhaps helping stabilize the etalon to a greater degree than the PST etalon:

SM90II RV disassembled.jpg
SM90II RV disassembled.jpg (485.46 KiB) Viewed 2878 times

Avoiding the possibility of torque-induced tilt is also why I chose a mechanical compression method for tuning that involves no rotational force applied to the etalon itself, and more or less applies uniform mechanical compression forces for the peripheral spacer compression concept to tune my LS35 etalon with success. Since the etalon CWL is nearly on-band to begin with (below left), only a small amount of pressure is required to get the etalon on-band (below right), and since no tilt is now needed, there is no banding issue to deal with. These etalons use the same orange foam rubber etalon seat, and additionally they have the customary silicone buttons spaced equally around both etalon plates:

Lunt 35 mech PT etalon changes.jpg
Lunt 35 mech PT etalon changes.jpg (408.32 KiB) Viewed 2878 times

If one has access to a Hydrogen spectrum tube, you can easily see how merely pressing with your finger on an etalon spacer will compress the spacer enough to change the etalon gap spacing and change the diameter of the etalon fringes.

Bob
Last edited by Bob Yoesle on Sun Feb 05, 2023 8:59 pm, edited 1 time in total.


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Re: Etalon PST problem - NEWS

Post by pupak »

That is a really precise interpretation of the given problem.


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Re: Etalon PST problem - NEWS

Post by Bob Yoesle »

I aimed my PST at the Sun and you can see the Sunlight reflected off the Etalon on the inside of the telescope tube and when I tune it on band the reflection moves because the Etalon is tilting... You can see it yourself by looking down the tube at Etalon as you turn the tuning ring and watch it tilt.
Hi David,

I noticed from your pictures that the line of sight has changed between the two pictures, which could explain in whole or in part the perceived etalon reflection changes on the inside of the PST tube attributed to tilting:

Image3.jpg
Image3.jpg (165.31 KiB) Viewed 2828 times

A better photographic test would be to fix the PST, the camera, and a bright distant light source (high power LED flashlight, etc.), and then observe how much possible tilt moves the internal reflection when tuning the etalon.

Best wishes,

Bob


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Re: Etalon PST problem - NEWS

Post by Valery »

In my present PST I noticed that banding (due to tilt) is different. Sometime, when only a little amount of tilt required to get to the H-a core, almost full sun disk seen in Ha and more or less uniform.
At higher barometric pressure and lower temp, the etalon require a severe tilt and as the result banding is significantly more apparent and the sweet band (belt) is narrower.
This behave can be seen only with a tilt tuned etalon.

I pointed a laser beam (laser collimator) on the PST etalon and tilted the etalon. And what? Reflected laser beam moved fully according to etalon tilt direction with 100% repeatability.

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Re: Etalon PST problem - NEWS

Post by DavidG »

Bob,
If you own a PST all you have to do is look down at the Etalon as you turn the ring and you easily see it tilting and as we know tilting is easy way to tune them
Valery's statement using a laser is again showing that the Etalon is tilting and that is mechanism of how it is tuned

If you wanted to use mechanical pressure tuning as the patent shows the Etalon needs to mount against a firm surface so pressure can be evenly applied. If not the air gap will not be even and the sweet spot will be very non uniform. Your not going to get any type of even pressure mounted in a foam ring that has non uniform air cells so it compress non uniformly and also allows the Etalon the tilt. You would have two competing methods of tuning, tilting which increase the light path through the Etalon and mechanical pressure that is decreasing it.

The guys that designed the PST needed an economical way to tune the Etalon and tilting it using piece a foam was brilliant and simple idea that works. The patent is not what they doing in PST. Don't make this more complicated then it is.

- Dave


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Re: Etalon PST problem - NEWS

Post by christian viladrich »

Further to Bob, I can add some information there ...

There is an easy way to check whether an etalon is tuned by tilting or compression, this is by using an Ha lamp :

http://astrosurf.com/viladrich/astro/in ... II-60.html

The interference pattern formed by the Ha lamp and the etalon is independant of the tilt of the etalon (since the incoming light is diffuse).

There are only three possibilities to have such an interference pattern changed (meaning changes in the radius of the rings):
- by changing the temperature of the etalon : this is the case with DayStar, SolarSpectrum, etc.
- by changing the etalon gap (i.e. compression) : this is the case of the SMIII RichView, and also .... the two PST I tested.
- by changing air pressure in the etalon gap : ex Lunt pressure tuned.

Looking at diffuse light from an Ha lamp, and playing with the rotating knob of the PST, you can see the changing of the interference pattern, which means the etalon is tuned by mechanical compression. You can even tabulate the CWL drift with how much rotation you give.

It is rather straighforward to calculate the pressure required to change the gap (hence the CWL) of the etalon. It is indeed rather small. I gave the calculation in an older post. And another Solar Chat amateur evaluated experimentaly the amount of pressure really put on the etalon. Calculation and experimentation was quite consistent.

There is also a more recent post describing a very nice improvement of the mechanism used to compress the etalon (using ball rolls as far as I remember ?). At the moment, I am afraid I don't remember the name of the very talented guy who made it.

So, there is no doubt that the PST is tuned by compression. It only takes an Ha light to confirm this.

And BTW, an Ha lamp is a very usefull tool to tune and test etalon too. There are also some posts about this.


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Re: Etalon PST problem - NEWS

Post by Bob Yoesle »

Hi Dave,

First, I've never owned a Ha PST.

My conclusions regarding the PST and compression tuning are based on the following information:

I too once thought that tilt-tuning an etalon worked by increasing the light path through the etalon. But this would seem to increase the CWL, which made no sense, as we all know tilting can only decrease the etalon CWL:
A seemingly plausible but wrong argument is that tilting makes the beam path longer, and that this must be compensated by a longer wavelength.
Tilt Tuning of Etalons RP Photonics

Having both tilt tuning to decrease the CWL and mechanical compression to do the same thing would make little sense.

Using the basic etalon equation, we can see that any tilt away from normal changes the cosine theta in a smaller direction, decreasing the CWL.

The argument that an etalon can't be mechanically compressed against a non-firm surface such as the foam rubber etalon seat is not born out by the fact this same material being used in all the non-PST Richview compression tuned etalons, my originally compression-tuned SM90 internal etalon, and my modified Lunt 35 etalon. I again would suggest getting a Hydrogen spectrum tube and apply some finger pressure to the etalon and see what happens ;-)

The very first PST etalons were 1.0+ A, and apparently were not designed for tilting:
We keep getting asked what is the difference between the PST and SM40 series. The most obvious difference is in the bandwidth. The SM/MS40 is <0.7Angstrom which is the ideal balance between prominence and surface detail. At <1.0A the prominences are favoured over surface detail although surface detail is still easily observable. The SM and MS 40 involve an external 40 mm etalon that is mounted on the front objective of the telescope. It is supported by a TMAX that can be "tilted" to optimise positioning. It can also be "tilted" off bandwidth in order to observe Doppler shifted events. The etalon is <0.7A. The instrument can be used for both visual and imaging purposes. The PST has an internal etalon with a 40 mm objective. It has no capacity for Doppler shifting.
Coronado Instrument Group Feb 2004

Shortly thereafter, an original Tucson Coronado personnel who has unimpeachable credentials and who would know from first-hand development has told me explicitly when tuning was first employed for the PST it was:
Compression for the original design at least, tilting would be difficult and given the cost… I haven’t seen anything disassembled since 2010 or so.
So unless something has changed since 2010, compression was and likely remains the PST tuning methodology. MEADE Coronado explicitly refers tot the PST tuning as "Richview."

PST diagram.jpg
PST diagram.jpg (29.49 KiB) Viewed 2344 times

The above information has also been confirmed by Christian Viladrich, who communicated privately with me the following in July 2021:
Hi Bob,

I am playing with two PST etalon (no lens), the SOlex and the Ha lamp.

I thought that the PST tuning was done by tilting the etalon. In fact,
observed with the Ha lamp, it appears clearly it is done by compressing
the etalon (just like the SMIII richview).

Is it what you have heard before?

The older PST etalon (maybe 97 ?) has some leakage in the blue light.
The newest (maybe 2010) has a different coating and no leakage.

Uniformity is bad.

More to come ...

Best wishes

Christian


Hi Bob,

Thanks for the link. The two PST I am testing have clearly some kind of compression tuning activated by the rotating knob. For sure, the knob does not tilt the etalon. Maybe, I'll have a closer look inside them, but there are not mine ...

I know one guy who has one of the first PST imported in France. There was no tuning at all.

Christian
Again, my postulate is that you and Valery are indeed observing tilting that occurs with the PST etalon. However, this is in all likelihood an untoward effect of the etalon being poorly secured - and per Mark Townley's tear-down - the etalon is free-floating, and that some torque or other force is being applied which results in the etalon tilt observed.

Best wishes,

Bob


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Re: Etalon PST problem - NEWS

Post by Bob Yoesle »

I just queried Brian Stephens (Tucson Coronado, Lunt Solar) regarding PST tuning:
It is Mechanical compression between a Teflon ring and silicone foam.


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Re: Etalon PST problem - NEWS

Post by pupak »

Thanks to everyone for trying to resolve the PST tuning issue. Although I have only minimal experience with the PST and will not own the hydrogen tube until the end of March, the design of the PST etalon shows quite clearly the pressure tuning and the tilt is a side effect of the etalon not being properly stored in the case. Coronado on PST saved money on the least suitable component. It's a shame.


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Re: Etalon PST problem - NEWS

Post by marktownley »

Good thread chaps!


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Re: Etalon PST problem - NEWS

Post by christian viladrich »

Finally, I got a hand on the post where I gave an estimation of the amount of pressure needed to tune the PST by 0.5A :

viewtopic.php?f=9&t=32638&p=300816#p300816


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Re: Etalon PST problem - NEWS

Post by pupak »

I am of the opinion that practice is 100x better than the best theory. Today I tried both PST etalons with my silicone pads and the stripes disappeared, the etalons can be tuned to a band, the homogeneity is not the best, but compared to the original pads it is a hundred times better. Since the pad prevents tilting, I believe the tuning was pressure tuned. Even with this pad, the tuning is sensitive and, above all, smooth without jump changes, as was the case with the original pad. Both etalons behave exactly the same. Bandwidth is weak average (1A), maybe even worse. In the next phase, I will try to connect them to DS with Quark or LS40. TZ3 and BF Quark were used.
Attachments
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Last edited by pupak on Tue Feb 07, 2023 3:34 pm, edited 1 time in total.


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Re: Etalon PST problem - NEWS

Post by christian viladrich »

Well done !
I guess a lot of guys here will be interested in these silicone pads ;-)


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Re: Etalon PST problem - NEWS

Post by DavidG »

On my PST's ( I have two ) the Teflon ring that comes in contact with the upper surface of the Etalon is on a slight angle. So it doesn't make contact evenly. So to reduce any possibility of tilting you might consider placing your silicon ring above the Etalon so the Etalon is against a hard surface and you can more even pressure.

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Re: Etalon PST problem - NEWS

Post by pupak »

christian viladrich wrote: Tue Feb 07, 2023 3:12 pm Well done !
I guess a lot of guys here will be interested in these silicone pads ;-)
I can make and send a plexiglass mold. The silicone can be bought anywhere in the world and there is no postage.


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Re: Etalon PST problem - NEWS

Post by pupak »

DavidG wrote: Tue Feb 07, 2023 3:55 pm On my PST's ( I have two ) the Teflon ring that comes in contact with the upper surface of the Etalon is on a slight angle. So it doesn't make contact evenly. So to reduce any possibility of tilting you might consider placing your silicon ring above the Etalon so the Etalon is against a hard surface and you can more even pressure.

- Dave
In order to prevent tilting, I put the etalon in a nylone cylinder in one case, which has a side clearance of less than 0.03 mm.
There was no noticeable difference compared to the pad itself.


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Re: Etalon PST problem - NEWS

Post by AndiesHandyHandies »

Hi

Listen to DavidG and in this case Valery.

Bob is wrong. And people who quote what some manufacturer employee? has told them has been taken up the garden path!
Someone was told they trim the orange pads with a surgical knife by hand!!!

Merlin finds the Coronado 90mms are tilt tuned. Using his spectrograph.

Just find a suitable bit of packaging foam to replace the degraded pads.

Cheers. Andrew.
Last edited by AndiesHandyHandies on Sun Feb 19, 2023 11:23 am, edited 1 time in total.


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Re: Etalon PST problem - NEWS

Post by AndiesHandyHandies »

Hi

The silicoln SOFT pads are just to hold the etalon against the teflon ring.

When you turn the adjuster it mechanically tilts the teflon ring which tilt tunes the etalon.

Cheers. Andrew.


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Re: Etalon PST problem - NEWS

Post by AndiesHandyHandies »

Hi

Whilst you show an orange ring some PSTs have just 3 small pads, and Merlin who has taken several apart has seen a doubled up one in a few cases. The doubling up to account for the leeway on one side because of the tilter gap. On the whole that seems to indicate they are just there to hold the etalon against the teflon ring and that the tuning mechanism is tilting the whole etalon holding steel ring.

Confirmed by Valery.

Cheers. Andrew.


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Re: Etalon PST problem - NEWS

Post by AndiesHandyHandies »

Hi

Also the foam would have to be of high homegenity to apply pressure very evenly to compress the mica spacers without introducing banding.

Cheers. Andrew.


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Re: Etalon PST problem - NEWS

Post by Bob Yoesle »

Hello Andrew,
Bob is wrong. And people who quote what some manufacturer employee?
I am not wrong. I queried and got direct responses from Bill Dean and Brian Stephens, who were not just "employees" - they were who originally designed the PST telescope at Coronado Tucson in the early 2000's and implemented the mechanical tuning mechanism - which is patented. With all respect to Valery and David, they did not design the telescope. The fact that tilt is detected does not necessarily mean it is the tuning methodology.

And if this is not enough, Christian's observations with the Hydrogen spectrum tube are the "nail in the coffin" for tilt tuning. This evidence is incontrovertible.
Someone was told they trim the orange pads with a surgical knife by hand!!!
I believe this may have came from Ken (Merlin66) and I have no idea who said this, nor can I vouch for its veracity. This may be what they now do in Mexico to mitigate the untoward tilting that does occur due to the less than ideal implementation (a loose etalon without radial support, and a rotational torque from the Teflon ring which increases with pressure) for the compression tuning, which permits the unintended tilting which apparently does occur. But this tilting is not the actual tuning methodology.

Lastly, I know from direct experience that the silicon foam is more than capable of supplying enough resistance to allow for mechanical compression. The internal 90 mm etalon for my 140 DS telescope was returned for CWL adjustment by applying additional peripheral pressure with the etalon resting on the orange silicon foam. I have implemented mechanical pressure against this same material with the thrust bearing tuning I used for the LS35 etalon, which has been successfully replicated by others - and it eliminated banding that results from tilt tuning. The RichView 90 mm etalon I have inspected also was similarly compressed against this material, as is the SM60 internal RichView etalon I have. The argument regarding the silicon foam homogeneity "unevenness," which seems to have been cited without any actual verification - needs to be thrown out as an unverified postulate and supposition used solely to support an erroneous conclusion.

What is needed is a paradigm shift among those who have become used to the idea of PST tilt tuning.

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Best wishes,

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Re: Etalon PST problem - NEWS

Post by AndiesHandyHandies »

Hi

Clearly the etalon does tilt when tuning.

Anyone who has played with a PST knows the centre of the sweet spot moves about as you turn the tuning ring in and out. And you need to approach the best position from one side.

And clearly from the damage to Pupaks orange foam rings they do apply some pressure.

I park my PST with the adjuster ring to the right as I believe the foam is under less pressure at that end. ????

We need a few people to fire a laser pointer at the front of a bare etalon with the reflection and direction of travel alligned with a ruler. And measure the full amount of tilt due to the tuner ring. CV can then calculate how much difference the tilt over the range makes to the tuning.

Its a commercial device made down to a price. I assume the first ones had the 3 little pads cut out of a sheet and then it was economic to have the orange rings made or a cutter?

One of the two components can have the larger tuning effect but the other will make some contribution as well.

Scientific method.

Cheers Andrew.


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Re: Etalon PST problem - NEWS

Post by pupak »

AndiesHandyHandies wrote: Mon Feb 20, 2023 9:27 am Hi

Clearly the etalon does tilt when tuning.

Anyone who has played with a PST knows the centre of the sweet spot moves about as you turn the tuning ring in and out. And you need to approach the best position from one side.

And clearly from the damage to Pupaks orange foam rings they do apply some pressure.

I park my PST with the adjuster ring to the right as I believe the foam is under less pressure at that end. ????

We need a few people to fire a laser pointer at the front of a bare etalon with the reflection and direction of travel alligned with a ruler. And measure the full amount of tilt due to the tuner ring. CV can then calculate how much difference the tilt over the range makes to the tuning.

Its a commercial device made down to a price. I assume the first ones had the 3 little pads cut out of a sheet and then it was economic to have the orange rings made or a cutter?

One of the two components can have the larger tuning effect but the other will make some contribution as well.

Scientific method.

Cheers Andrew.
I have two PSTs modified in such a way that the etalon cannot be tilted in the case and is adjusted only by pressure, so your theory is interesting, but it is in direct contradiction with practice, so it is useless.
Petr


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Re: Etalon PST problem - NEWS

Post by AndiesHandyHandies »

Hi

But you are referring to modded etalon holders.

I am saying for the actual PST that it can be pressure tuned but several people report that the etalon does tilt whilst being tuned, and if it is tilting it will affect the tuning in some way, might be small.

Cheers. Andrew.


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Re: Etalon PST problem - NEWS

Post by pupak »

From the beginning, we are talking about the principle of PST tuning, not about the secondary effects of a bad design of the etalon.


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Re: Etalon PST problem - NEWS

Post by Valery »

pupak wrote: Mon Feb 20, 2023 12:30 pm From the beginning, we are talking about the principle of PST tuning, not about the secondary effects of a bad design of the etalon.
Andy is correct. The original tuning method in PST is tilting the etalon.
You just REDESIGNED the PST tuning system by changing the princip being inspired by Bob's invention in his LS35. Bravo!


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Re: Etalon PST problem - NEWS

Post by AndiesHandyHandies »

pupak wrote: Mon Feb 20, 2023 12:30 pm From the beginning, we are talking about the principle of PST tuning, not about the secondary effects of a bad design of the etalon.
Sorry I wandered down a seperate path.


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Re: Etalon PST problem - NEWS

Post by pupak »

My only motivation was to replace the crappy silicone pads that the etalons didn't work well with. I made new ones and the etalons became usable. I tried the cylindrical case just to make sure that the etalon is not actually tilting but pressure tuned. I believe that only one method should be used for tuning, pressure or tilt. The combination of both is quite unusable for real use. Taking into account the fact that the tilt range is about 5 degrees in the LM40 and much smaller in the PST, since a torn pad will cause uneven pressure rather than significant tilt, tuning by changing the pressure is a logical conclusion. If the primary intention of the PST was to tune by tilting, the design is very poorly thought out.


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Re: Etalon PST problem - NEWS

Post by Valery »

pupak wrote: Tue Feb 21, 2023 7:13 am My only motivation was to replace the crappy silicone pads that the etalons didn't work well with. I made new ones and the etalons became usable. I tried the cylindrical case just to make sure that the etalon is not actually tilting but pressure tuned. I believe that only one method should be used for tuning, pressure or tilt. The combination of both is quite unusable for real use. Taking into account the fact that the tilt range is about 5 degrees in the LM40 and much smaller in the PST, since a torn pad will cause uneven pressure rather than significant tilt, tuning by changing the pressure is a logical conclusion. If the primary intention of the PST was to tune by tilting, the design is very poorly thought out.
"If the primary intention of the PST was to tune by tilting, the design is very poorly thought out."

Absolutely! This clearly reflects in the price of PST telescopes.

If the tuning was really a compression, then, I believe it will be realized very much like you did it.

And, I am very satisfied that you applicated Bob's Y. invention with LS35 to your PST etalons.
I will gladly by the PST etalon cradle you have invented. And I believe many many others will be interested in it too.
In any case, thank you a lot. If I will not be able to buy such a cradle, I can make something similar to your one.


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