Small Etalon Improvement For Only $15 USD (13 Euros)

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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Bastelhannes wrote: Thu Sep 16, 2021 6:49 am Did anyone play with piezo actors so far? Yes, they are a lot more expensive...
Nope, what you read is what has happened so far with this, it's a new thread.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Hmmm.

This is not as straight forward with a Lunt50C. As noted previously the ERF is tilted, as is the ERF retaining ring, which then sits proud of the inner face of the ERF housing (red screw on section). This is remedied by putting a riser plate around the ERF retaining ring to create a flat surface for the bearing to sit on.

There is no more than 5mm clearance between the inner face of the etalon housing and the face of the etalon. Tight, but doable.

Now, here comes my 'doh' moment. The edge of the etalon housing (the black bit with the tilter on visible after the red housing is screwed off) sits maybe 1/2mm proud of the face of the etalon. Soooooo, my 78mm bearing and washers rides the edge of the etalon housing, not the face of the etalon.

Back to the drawing board.

I need a bearing that is smaller than the 78mm I ordered - something more like 74mm (simplybearings.co.uk are going to love me :lol: ).

Doable, just different component parts...


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Ok, sometimes you just need to sleep on something... Think I have a solution for this, just hope i've got enough laser cut rubber left to make a different sized gasket. Should be able to use existing bearing without buying new one...

Guess this is my project for the weekend now...


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Rusted »

Is there anything to gain from using PTFE on PTFE to lower the torque on the etalon and rubber ring?
It might make for a much simpler bearing with thickness becoming a free choice compared with needle roller thrust bearings.

BTW: Are the needle rollers tapered to match the difference in turning radius along their length?


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Rusted wrote: Fri Sep 17, 2021 6:10 am Is there anything to gain from using PTFE on PTFE to lower the torque on the etalon and rubber ring?
It might make for a much simpler bearing with thickness becoming a free choice compared with needle roller thrust bearings.

BTW: Are the needle rollers tapered to match the difference in turning radius along their length?
Regards the PTFE tape - honestly no idea?

Regards the bearings being tapered, visually, and bear in mind each roller on the ones I purchased is about 5mm long and 1mm wide (estimate), they don't look to be tapered, but without doing the maths I don't know how much taper you would expect to see in the geometry of it all.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

An update on this with my Lunt50C:

So I laser cut a new rubber washer that sits between the face of the etalon and the back side of the bearing, this works and the bearing sits above the etalon housing which is slightly proud of the face of the etalon. That problem solved...

Next work around... There really isn't many mm of space between the etalon face and the back of the ERF housing, maybe 4mm, and this wasn't helpful in fitting everything in. However, the ERF cell screws into the red anodised barrel of the etalon housing. In true fashion with solar kit the thread is 'locked' on this with a couple of liberal smears of silicone seal. Picking this out with a pin to free the threads, and then using a lens spanner you can back off the ERF cell housing towards the front of the scope to give more space internally.

Soooo, now, from the face of the etalon I have rubber washer, bearing, metal washer, rubber riser plate around the ERF cell to give a flat surface. I woke this morning to the sun shining around the edge of the bedroom curtains, it's not going to be a wall to wall sunshine day as there is cloud floating around but I am optimistic I should get to test it... Watch this space!

Mark


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

And the proof of the pudding... My Lunt LS50C etalon needs no tilt for it to be on band, see pic below:

ImageHa-FD-SS-BW by Mark Townley, on Flickr

Using the compression method described in this thread indeed shifts the centre line of the tuning, but in my case as the etalon needs no tilt the method is not needed. Pic below shows with compression applied.

ImageHa-FD-SS-Bob-Mod-BW by Mark Townley, on Flickr

So, morale of the story, this method works really well, but only if you are having to tilt your etalon to bring it on band.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bastelhannes »

Because I am not aware, if the Lunt etalon is a different type compared to the PST etalon: would it be worth to take some time to try this with PST etalon? If Mark punches my idea balloon again with his reality check needle.. I could save some time, if this idea is too ridiculous... (No offend Mark, I really appreciate your knowledge and am happy, that people like you share your knowledge. In my case it's like having a fantastic idea while being drunk and the next morning I discover being sober: what a sh't...)


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Bastelhannes wrote: Sun Sep 19, 2021 6:05 am Because I am not aware, if the Lunt etalon is a different type compared to the PST etalon: would it be worth to take some time to try this with PST etalon? If Mark punches my idea balloon again with his reality check needle.. I could save some time, if this idea is too ridiculous... (No offend Mark, I really appreciate your knowledge and am happy, that people like you share your knowledge. In my case it's like having a fantastic idea while being drunk and the next morning I discover being sober: what a sh't...)
Tee hee hee! :lol:

The PST etalon is tuned by compression, so the same principle is already happening here.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

Those are very good demonstration images Mark!

The methodology works, but as you note the etalon is already on-band without tilt, and compression only further blue-shifts the CWL.

Applying heat via some sort of electrical resistance similar to a dew heater, or the Sun itself (ERF removal), might serve to warm the etalon feet/spacers sufficiently to raise the CWL and allow the etalon to have "room" for compression tuning. A longpass filter could be employed for environmental protection of the front etalon surface, and perhaps give a bit of “greenhouse effect” for etalon warming.

As with any heat applied to an etalon, you’d have to give it a bit of time for the etalon to stabilize thermally for optimum results. And as I discovered with the DSF100 filters, the larger the etalon, temperature stabilizing becomes more difficult and takes longer, and etalon gap uniformity may not be as easily obtainable. Then again there's a big difference between 50 mm and 100 mm...


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by AndiesHandyHandies »

Hi

I think in the thread close by thread we have established that the PST is tilt tuned.

Cheers. Andrew.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by AndiesHandyHandies »

Hi

Are these the only tuning methods available:

Tilt tuning, to make the space between the plates on axis longer - PST

Heating the mica spacer - Quark

Pressurising the air in the etalon air gap to change the refactive index - Lunt

Patented RichView tuning using novel spacers and actuators to mae the space smaller - Coronado DS90.

And so the whole no of wavelengths of light which will fit in and result in constructive interference

For all of these a comb filter is needed to pick out the required h-alpha wavelength, and reject off band wavelengths where different nos of waves fit in the gap.

Professionals seem to tilt the Fabray-Perot etalons to tune them.

The patent seems to preclude any other commercial H-Alpha filters using compression and I cannot find any other reference to compression tuning.

Cheers. Andrew.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

I think in the thread close by thread we have established that the PST is tilt tuned... Patented RichView tuning using novel spacers and actuators to mae the space smaller - Coronado DS90... The patent seems to preclude any other commercial H-Alpha filters using compression and I cant find any results for compression tuning.
Hi Andrew,

The "rich-view" spacer feet are not "novel." They are fused silica as is used by Coronado, Lunt, and Solarscope.

Those denying the compressibility of fused quartz are mistaken. I know it sounds counter intuitive that compressing the thin glass spacer feet could be accomplished in order to tune an air-spaced etalon - but that is the reality. The gap spacing is so sensitive that only small gap changes results in a CWL shift. And these spacers, even though made of low-expansion materials, are sensitive to both a thermal expansion and mechanical compression because no material is impervious to compression or thermal expansion. The quality and uniformity of the spacers are just as important to etalon performance as the etalon plates themselves.

1. I have proved mechanical compression tuning works on a Lunt etalon quartz spacers conclusively with the etalon fringes shown in the first post in this thread. Mark's post above confirms this. Before I implemented vacuum tuning, my DS140/90 telescope's internal quartz-spacer etalon was compression tuned around the periphery.

2. Coronado has implemented this compression methodology over the years with quartz spacer etalons - first with their internal double stacking modules when based in Tucson, and then with the SMII and SMIII "rich view" tuning implemented by MEADE Coronado. It is widely known the PST etalon is usually tuned via edge compression (some early PST's may have been tilt-tuned), and edge compression is shown in the original 2006 patent (link below). Christian Viladrich has confirmed central compression pressure tuning for the "rich view" etalons. Disassembly of the RV etalon can plainly see how it is accomplished (imperfectly) with mechanical pressure applied to the central spacer area.

SM60II richview etalon.jpg
SM60II richview etalon.jpg (115.2 KiB) Viewed 5783 times
Note the pressure adjustment bolt in the center of the internal SM60II collimator lens, which if over tightened can actually fracture the collimator lens.


3. "Professionals" generally seem to use piezo-electric tuning for the most precise applications of fine-tuning etalons, and this is indeed making very small changes to the etalon gap spacing as is done with mechanical compression.

4. Mechanical compression tuning was patented by Lunt et.al. at Coronado in 2006. US patents are generally in effect for 20 years (this one expires in 2024). Lunt may then opt to implement this as well for their front tilt-tuned etalons. Nothing precludes DIY implementations for non-commercial applications.
Last edited by Bob Yoesle on Tue Sep 21, 2021 5:10 pm, edited 1 time in total.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by AndiesHandyHandies »

Bob Yoesle wrote: Tue Sep 21, 2021 2:10 pm
I think in the thread close by thread we have established that the PST is tilt tuned... Patented RichView tuning using novel spacers and actuators to mae the space smaller - Coronado DS90... The patent seems to preclude any other commercial H-Alpha filters using compression and I cant find any results for compression tuning.
Hi Andrew,

The "rich-view" spacer feet are not "novel." They are fused silica as is used by Coronado, Lunt, and Solarscope.

Those denying the compressibility of fused quartz are mistaken. I know it sounds counter intuitive that compressing the thin glass spacer feet could be accomplished in order to tune an air-spaced etalon - but that is the reality. The gap spacing is so sensitive that only small gap changes results in a CWL shift. And these spacers, even though made of low-expansion materials, are sensitive to both a thermal expansion and mechanical compression because no material is impervious to compression or thermal expansion. The quality and uniformity of the spacers are just as important to etalon performance as the etalon plates themselves.

1. I have proved mechanical compression tuning works on a Lunt etalon quartz spacers conclusively with the etalon fringes shown in the first post in this thread. Mark's post above confirms this. Before I implemented vacuum tuning, my DS140/90 telescope's internal quartz-spacer etalon was compression tuned around the periphery.

2. Coronado has implemented this compression methodology over the years with quartz spacer etalons - first with their internal double stacking modules when based in Tucson, and then with the SMII and SMIII "rich view" tuning implemented by MEADE Coronado. It is widely known the PST etalon is usually tuned via edge compression (some early PST's may have been tilt-tuned), and edge compression is shown in the original 2006 patent (link below). Christian Viladrich has confirmed central compression pressure tuning for the "rich view" etalons. Disassembly of the RV etalon can plainly see how it is accomplished (imperfectly) with mechanical pressure applied to the central spacer area.


SM60II richview etalon.jpg

Note the pressure adjustment bolt in the center of the internal SM60II collimator lens, which if over tightened can actually fracture the collimator lens.


3. "Professionals" generally seem to use piezo-electric tuning for the most precise applications of fine-tuning etalons, and this is indeed making very small changes to the etalon gap spacing as is done with mechanical compression.

4. Mechanical compression tuning was patented by Lunt et.al. at Coronado in 2006. US patents are generally in effect for 20 years. Lunt may then opt to implement this as well for their front tilt-tuned etalons. Nothing precludes DIY implementations for non-commercial applications.
Hi

Thanks for the clarification.

1. Can I tell from my serial no if my PST if it is an early one, it has the rusted yellowish coating. Do the compression tuned PSTs still have the orange foam?

2. It seems the Patent I looked at is different to the actual RichView implementation?

3. At a quick look.

4. I cannot get the link to work. Does it refer to novel materials? This is the one I looked at. https://patents.google.com/patent/US20050078906

So if you have an old tilted PST can it be converted to pressure tuned, and is one way of tuning superior to the other?

Thanks. Andrew.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

Hi Andrew,

Item 1. I am not familiar enough with the PSTs to give you guidance here (compression tuning of the PST goes back at least to 2017 if not further), and I similarly can't tell you how easy it would be to convert a possible tilt tuned PST etalon to a compression tuned etalon. Theoretically, a compression tuned etalon would be better if you can uniformly apply pressure that maintains a good etalon gap uniformity verses a tilt etalon. But as with most things there are a lot of variables in the execution that will affect the outcome. Personally I would leave the OEM tuning in place for the PST - which likely is already compression tuned.

Item 2. The patent is generally referring to compression of the etalon spacers, while the "rich-view" implementation applies compression only to the central spacer in the SMII and SMIII. However, in 2017 Meade Coronado also refers to the PST as being "rich-view" tuned, which only involves peripheral spacers. So "rich-view" is really a generic term applied to any mechanical compression methodology used by Meade Coronado.

Item 4. The link is to a pdf file that opens fine in Chrome, here's the source link, and you can see the pdf by clicking on that download option. This is the final approved patent by the patent examiner, your link is to the patent application.

I quoted you with regard to the term "novel." The patent refers to both conventional etalons (as I have used in this thread):
In the preferred embodiment of the invention, the device consists of a housing that includes a hollow cylindrical component and a cap that define an interior space adapted to receive a conventional air-spaced etalon [emphasis added]. The cylindrical component and the cap are coupled by means of a very finely treaded connection which, through rotation of the cap, allows the axial adjustment of the length of the interior space and the corresponding uniform compression of the etalon to fine tune the optical length of its cavity.
as well as "individual pressure actuators" (e.g. the SMII/III "rich-view" method), and use of other compression methods and materials.
Last edited by Bob Yoesle on Tue Sep 21, 2021 6:27 pm, edited 1 time in total.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bastelhannes »

Bob,

Thank you very much for all the details and the links to the documents.

Looks like Mark got a new "reality needle" competitor...


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Bastelhannes wrote: Tue Sep 21, 2021 5:51 pm Looks like Mark got a new "reality needle" competitor...
:lol:


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bastelhannes »

Bob,

did you, by accident, measure the movement you induced to the etalon by pressure? This would be very interesting to evaluate a fitting piezo actor...


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by AndiesHandyHandies »

Hi

Merlin in the other thread active now say all the PSTs he has taken apart had the orange ring in.

If they all have the two litle feet on one side as in Marks PST diss-assembly video shows then it seems clear to me they are tilt tuned.

The double stack Coronado filter with richview are compression tuned as well as tilted. Merlin checked all this with his spectro-graph.

Cheers. Andrew.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Carbon60 »

Just to add to the previously described success with my Lunt 35 on my 150mm/Lunt 35 DS mod (result shown earlier in this thread) and Mark's Lunt 50, here's my Lunt 60 front Etalon mod using Bob's compression method.

I used the same components, just larger (60mm inner diameter/85mm outer).
Lunt 60 Etalon_Bearing and Washers.JPG
Lunt 60 Etalon_Bearing and Washers.JPG (116.86 KiB) Viewed 5714 times
The washers were bonded onto fabric (piece of blackout curtain) to provide a soft surface to mate against the glass and inner surface at the front of the removable red etalon housing.
Lunt 60 Etalon_Washer Bonding.JPG
Lunt 60 Etalon_Washer Bonding.JPG (92.46 KiB) Viewed 5714 times
I cut around the inner and outer perimeters once cured to remove the excess fabric, leaving a bit of a boarder around the top washer to help hold it in place during assembly into the red etalon housing.
Lunt 60 Etalon_Components.JPG
Lunt 60 Etalon_Components.JPG (104.67 KiB) Viewed 5714 times
Lunt 60 Etalon_Bearing Assembly.JPG
Lunt 60 Etalon_Bearing Assembly.JPG (105.79 KiB) Viewed 5714 times
The housing was screwed into place leaving a few threads to fine tune when on the scope.
Lunt 60 Etalon.JPG
Lunt 60 Etalon.JPG (93.66 KiB) Viewed 5714 times
As with my Lunt 35 and as Mark has said with his 50, on-band can easily be achieved without any tilt by simply screwing the housing down on the threads. Too far and it goes off-band, as Mark has shown.

This has really helped get better FDs with my triple stacked Lunt 60 which otherwise suffers from banding. This enabled me to take this multi-pane mosaic with little to no witness lines between panes; something that was really difficult beforehand.

Image20210920_Ha_FD_Mono by Stuart Green, on Flickr

I'll obviously run further trials to give it a thorough test, but this and my Lunt 35 mods are looking good so far.

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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

That's a fantastic mosaic image Stu! And thanks for posting your implementation pics - very helpful to see the fabric centering method you described earlier. Another refinement could be a thin shim of some sort to keep the needle bearing itself centered in the housing and on the bearing races.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Valery »

Bob Yoesle wrote: Tue Sep 21, 2021 5:01 pm
However, in 2017 Meade Coronado also refers to the PST as being "rich-view" tuned, which only involves peripheral spacers.
Hi Bob,

They referred to the Double Stack 40mm external etalon being RichView tuned. Not to internal tilt tuning etalon.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Carbon60 »

Bob Yoesle wrote: Wed Sep 22, 2021 11:53 am That's a fantastic mosaic image Stu! And thanks for posting your implementation pics - very helpful to see the fabric centering method you described earlier. Another refinement could be a thin shim of some sort to keep the needle bearing itself centered in the housing and on the bearing races.
Hi Bob,
Good thought about a shim, but I think once the compression load is applied through the stack the bearing is effectively held in place by friction. I haven’t seen any evidence of it shifting yet, but will keep an eye on it.

Stu.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

Hi Bob, They referred to the Double Stack 40mm external etalon being RichView tuned. Not to internal tilt tuning etalon. Valery
Hi Valery. The reference to RichView tuning I cited was the PST's internal etalon, then called a "30 mm," which in reality is the same as always 20 mm clear aperture etalon. It is tuned via mechanical compression, which shifts the natively high CWL blueward to be on-band just as occurs with a tilt tuned front-mounted etalon.
The compression system works because it can squeeze the feet due to their Youngs modulus... The physical compression of these systems was used early on as a way of tuning the etalon to the desired CWL. It was abandoned after a few years due to the inability to effectively compress the center foot and the outer feet uniformly. The product was the MaxScope 70. The compression system was re-introduced for the PST. A system that did not have a center obstruction to the etalon to deal with. (Andy Lunt)
Hi Bob, Good thought about a shim, but I think once the compression load is applied through the stack the bearing is effectively held in place by friction. I haven’t seen any evidence of it shifting yet, but will keep an eye on it. Stu.
Hi Stu. Good to hear, but I will note that I completely back off the compression on the LS35 so as to maintain the resilience of the silicone support ring when the scope is not in use, and therefore the smaller diameter of the roller bearing and un-secured bearing races do have some ability to shift slightly within the etalon cover assembly...


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Martin_S »

This has been a great thread, many thanks to all the contributors to this thread.
I'm about to try this on my LS50F etalon. I will be trying a slightly different method of assembly.

I have around 100 ,65mm diameter x 1.5mm thick O rings that were sent by mistake on Ebay, so I thought I would try one instead of the rubber gaskets that have been used in previous
posts.

The etalon housing is slightly higher than the top face of the etalon glass by about .5mm, so I'm hoping that this O ring will put even pressure onto the etalon. I'm not sure how much the O ring will compress once everything is assembled. If it works it should be a lot easier than custom cutting rubber gaskets.

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20211127_111933.jpg
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Excellent, let us know how you get on Martin.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by christian viladrich »

A lot of excellent information here. Thanks for sharing !


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

Hi All,

Since it's been a while, I was wondering how these mods held up. Are you still using them? Any need to replace the rubber/felt elements? Any troubles with decontacting? I am considering doing this for my Lunt 40mm etalons.

Best,
Derek


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Since the etalon from PST was also mentioned here, I have a question. It is possible that the rubber pads damaged in this way ensure the correct functioning of the etalon, or there is some hidden intention. Thanks for every opinion.
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

First, let me say I have never owned or inspected an Ha PST. I have viewed Mark's video on the disassembly of a PST etalon chamber.

It would seem these defective seating pads would result in uneven mechanical pressure to the etalon peripheral spacers, and even result in some tilt. Indeed, any tilt that may be occurring with the PST seems to be a fault of the compression tuning implementation. I note in Mark's video there is quite a bit of slop that can occur in the etalon chamber, as the etalon appears completely free to float on the orange foam rubber ring as the nylon/plastic O compression ring is screwed down. I think the less friction from a roller bearing method would be better - maybe you can give that a try with the PST etalon.

In the larger SM90II rich view etalon I had a chance to play with, the lower etalon plate was fixed in its cell with the usual silicon blobs around the side to keep it from tilting. The PST etalon has no such fixation. This might be giving some of the unevenness (the sweet band) from unintended tilt that can be seen with PST etalons at times?

Another issue with the PST might be the compression ring has a bit of friction, and might therefore skew the etalon a bit because it is not secured in any way as compression is applied. This might be where the roller bearing methodology could be a better implementation for tuning of the PST etalon.

I any case I would be replacing those foam rubber gaskets with a more uniformly thick solution. This would seem to be even more important with the PST, since unlike the Lunt etalons, there are none of the silicone buttons around the side of the etalon plates that help secure it and maintain its position without any appreciable tilt as compression is applied.

Bob


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Bob Yoesle wrote: Tue Jan 31, 2023 3:00 pm First, let me say I have never owned or inspected an Ha PST. I have viewed Mark's video on the disassembly of a PST etalon chamber.

It would seem these defective seating pads would result in uneven mechanical pressure to the etalon peripheral spacers, and even result in some tilt. Indeed, any tilt that may be occurring with the PST seems to be a fault of the compression tuning implementation. I note in Mark's video there is quite a bit of slop that can occur in the etalon chamber, as the etalon appears completely free to float on the orange foam rubber ring as the nylon/plastic O compression ring is screwed down. I think the less friction from a roller bearing method would be better - maybe you can give that a try with the PST etalon.

In the larger SM90II rich view etalon I had a chance to play with, the lower etalon plate was fixed in its cell with the usual silicon blobs around the side to keep it from tilting. The PST etalon has no such fixation. This might be giving some of the unevenness (the sweet band) from unintended tilt that can be seen with PST etalons at times?

Another issue with the PST might be the compression ring has a bit of friction, and might therefore skew the etalon a bit because it is not secured in any way as compression is applied. This might be where the roller bearing methodology could be a better implementation for tuning of the PST etalon.

I any case I would be replacing those foam rubber gaskets with a more uniformly thick solution. This would seem to be even more important with the PST, since unlike the Lunt etalons, there are none of the silicone buttons around the side of the etalon plates that help secure it and maintain its position without any appreciable tilt as compression is applied.

Bob
I made a test precision silicone pad that will ensure the placement of the etalon in the axis of the case. If the sun ever shines here again, I'll try it. :)
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

That looks great!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

I love how additive manufacturing has benefitted the world of solar!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

I like the idea of pressure tuning the LS40. I would like to modify the LS40 to fit with the assembly.
I assume that the ERF is useless.
Does anyone know what the underside of the etalon rests on? Is there a stop, or does the etalon in the case only hold the silicone on the edges? If there is no lower support surface, then the compression of the etalon must be quite uneven, because the silicone is applied there rather irregularly.
I am mainly interested in reducing the dimensions and reducing the weight of the etalon.
Thanks for every opinion.
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Cunning. Thst works well!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

I'd assume the LS40 is nearly identical to the LS35 (see first post of this thread), and the LS40 etalon will be supported equally and uniformly around the perimeter of each etalon plate, and the etaon is seated on the same type of silicon foam rubber pad as the PST and other etalons.

The ERF is an RG610 or 630 with dielectric IR blocking coatings, in a tilted ERF cell. This is required for all front mounted etalons. It's only useless if you are doing a DIY internal etalon implementation. But even there the ERF cell might serve a useful purpose for ancillary ERF duty, or support a circular polarizer if doing a DS internal implementation within a collimator or telecentric lens system,

I would be concerned that there will always be some friction from the Teflon/silicon/whatever ring(s) that will apply some level of torque that increases with compression to the etalon, and might have some detrimental effects as it does with the PST etalon. This is greatly reduced if not totally eliminated with the thrust bearing implementation which was originally posted about, and therefore would seem the superior method of applying any form of etalon compression tuning.
Next was deciding how to apply uniform pressure, and I struck upon the idea to use a very thin needle trust bearing with even thinner thrust races that would total only 4 mm thick when combined, which also had the appropriate inside and outside diameters, and leaving plenty of room for a thin (~ 2 mm) rubber gasket to apply uniform pressure to the etalon periphery. This would therefore translate rotational movement in to a uniform axial movement and pressure without any torque applied to the rubber gasket or etalon face.
Bob ;-)


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Your arguments are very reasonable. I understand that you want to avoid rotational force when tuning, but there are two circumstances where I don't think the use of a needle bearing is necessary.
First of all, no one knows what torque could damage the etalon. I guess this is just speculation or am I wrong?
Secondly, the rotational moment is very small, because it is only a fraction of the force in relation to the force acting axially, because the coefficient of friction between teflon, nylon, silicone and glass is very small, when we consider that the axial force is in units of Newtons, then the rotational moment comes out in mNm. The etalon is glued to the tube with silicone in several places and this effectively prevents the individual parts of the etalon from turning relative to each other due to a small rotational force.
If the etalon had a significantly larger diameter and was not divinely fixed, the needle bearing is really ideal, but it is probably not necessary for this particular design.
I'm not asking anyone to abandon your tried-and-true approach, just offering an alternative solution.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Valery »

Bob Yoesle wrote: Sat Feb 11, 2023 12:54 am I'd assume the LS40 is nearly identical to the LS35 (see first post of this thread), and the LS40 etalon will be supported equally and uniformly around the perimeter of each etalon plate, and the etaon is seated on the same type of silicon foam rubber pad as the PST and other etalons.

The ERF is an RG610 or 630 with dielectric IR blocking coatings, in a tilted ERF cell. This is required for all front mounted etalons. It's only useless if you are doing a DIY internal etalon implementation. But even there the ERF cell might serve a useful purpose for ancillary ERF duty, or support a circular polarizer if doing a DS internal implementation within a collimator or telecentric lens system,

I would be concerned that there will always be some friction from the Teflon/silicon/whatever ring(s) that will apply some level of torque that increases with compression to the etalon, and might have some detrimental effects as it does with the PST etalon. This is greatly reduced if not totally eliminated with the thrust bearing implementation which was originally posted about, and therefore would seem the superior method of applying any form of etalon compression tuning.


Bob ;-)
Thanks, Bob.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

I tried to design a solution that does without the needle bearing and does not transfer the torque to the etalon.
The etalon is glued into the case with 6 tapes approx. 8 mm wide. The gap between the case and the standard is 1.5 mm. If I fit a duralumin ring (2) snugly into the housing with cutouts that fit into the gaps between the silicone strips and have cutouts for the silicone washer (1) on the top edge, this will prevent any torsional stress on the etalon during tuning.
The ring is firmly seated in the frame of the etalon and the silicon washer is anchored in the cut-outs of the ring, only the axial force generated by the threaded cylinder is transmitted.
This solution is more complex to manufacture than Bob's, so it is only suitable for someone with mechanical skills or a lot of friends.
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Since for me, realization is usually only hours away from the idea, the pressurized LM40 is ready for tests. The pressure is solved by a Teflon toroid, which is stored in a groove and lined with a precise silicone pad. In order for Bob to sand me less :) , the toroid is still coated with a small layer of Teflon paste on the side in contact with the glass. Friction should really be minimal. Tuning from the outside is currently via two M3 screws, which have a range of about 90 degrees. Inside there are 4 threads at 90 degrees, so finding the optimal position should not be a problem. I'm really curious about it. Hopefully the one day's work won't be for nothing. ;)
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

Here is another version for the Lunt 40mm. Try as I might, I could not find thrust bearings to fit the 40mm etalon. Instead, I ended up going with 2-3 PTFE washers 2mm in thickness, 55mm OD and 45mm ID, centered in the cover using 3 pieces of velcro tape - under $10 USD total cost. The idea is that the two washers slide against each other, reducing rotational forces on the etalon. (The washers were : MECCANIXITY PTFE Flat Washers 55mm OD 45mm ID 2mm Thick Flange Gasket, White Pack of 5)

Seems to work well via hydrogen lamp, but clouds for the next week so no test under the sun yet… Images below.

-Derek
CompressionTuneLunt40.png
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

Well done!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

I’m a little afraid of taking apart my etalon. I always end up touching something or doing something unintentionally that screws something up. I’m really afraid of decontacted etalons since they are so pricey to fix. Am I being too cautious or paranoid? How hard or easy is this mod?

Has anyone tried this out on a 90mm SM1?


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

hopskipson wrote: Wed Jun 14, 2023 11:26 pm I’m a little afraid of taking apart my etalon. I always end up touching something or doing something unintentionally that screws something up. I’m really afraid of decontacted etalons since they are so pricey to fix. Am I being too cautious or paranoid? How hard or easy is this mod?

Has anyone tried this out on a 90mm SM1?
If you don't feel confident mossing, you really shouldn't do so!

I've thought about trying it with my SM90 etalon, but never got round to it.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

Oak wrote: Sun Jun 04, 2023 7:06 pm Here is another version for the Lunt 40mm. Try as I might, I could not find thrust bearings to fit the 40mm etalon. Instead, I ended up going with 2-3 PTFE washers 2mm in thickness, 55mm OD and 45mm ID, centered in the cover using 3 pieces of velcro tape - under $10 USD total cost. The idea is that the two washers slide against each other, reducing rotational forces on the etalon. (The washers were : MECCANIXITY PTFE Flat Washers 55mm OD 45mm ID 2mm Thick Flange Gasket, White Pack of 5)

Seems to work well via hydrogen lamp, but clouds for the next week so no test under the sun yet… Images below.

-Derek

CompressionTuneLunt40.png
Hi Derek
Did you ever get the chance to test your design? I just got a Lunt 40 and limited testing looks positive.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

Briefly though wildfire haze but the results were very good. No more sweet band in double stack. Is your 40mm fairly uniform?


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

Oak wrote: Tue Jun 20, 2023 12:40 am Briefly though wildfire haze but the results were very good. No more sweet band in double stack. Is your 40mm fairly uniform?
I just got it today and had a brief time with a very stiff photo tripod. It looks pretty good from what I saw today. The full disk looked uniform on band. Looks like I’m in for a rough patch of weather for the next 8 days. :?

So you’re pretty happy with the operation? Do you notice any sticking of the washers or is it smooth threading?

Thanks for the update.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

hopskipson wrote: Tue Jun 20, 2023 2:03 am
Oak wrote: Tue Jun 20, 2023 12:40 am Briefly though wildfire haze but the results were very good. No more sweet band in double stack. Is your 40mm fairly uniform?
I just got it today and had a brief time with a very stiff photo tripod. It looks pretty good from what I saw today. The full disk looked uniform on band. Looks like I’m in for a rough patch of weather for the next 8 days. :?

So you’re pretty happy with the operation? Do you notice any sticking of the washers or is it smooth threading?

Thanks for the update.
Yes I am happy with it during my brief observing session. Reduced banding in double stack. I did not notice any sticking when I tightened the housing. I carefully cleaned the washers and tested how they slid against each other under pressure before using them - very little detectable friction. I was adjusting VERY slowly under diffuse illumination from the hydrogen lamp to watch the CWL shift. I haven't decided if it is better to loosen between uses or keep the compression in place. The etalon does sit on a foam or rubber ring that is somewhat compressible.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

My preference it to loosen when not in use, as this will allow the foam ring to "relax" back to "normal" and relieve any stress on the silicone buttons that constrain the the edge of the etalon plates.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

I’m thinking of doing this to my SM1 90. Should I be concerned about not compressing the central spacer?


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These pretzels are making me thirsty! (C.C.)
The Quark introduced me to this wonderful side of the hobby and the sun hasn’t disappointed yet.
Solar Equipment: Solar Spectrum RG-18 0.3A, Coronado Solarmax 90mm etalon Isle of Man SN-001, Tuscon SN-380 and Meade SM2, Lunt LS80 DS, Quark Chromosphere, Lunt 2" wedge, 2-Lunt CaK II 1200, Baader 3.8 and 5.0 solar film in 208mm cells, and 3D printed Sol'Ex SHG, Lunt 40mm
Coming Soon: Solar Spectrum CaK II <1A filter
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