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 298 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 229 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 229 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 229 times
Lunt 60 Etalon_Bearing Assembly.JPG
Lunt 60 Etalon_Bearing Assembly.JPG (105.79 KiB) Viewed 229 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 229 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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