Dream come true!

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Re: Dream come true!

Post by Solar B »

All good :)

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Re: Dream come true!

Post by Bob Yoesle »

Getting a little OCD now... More waiting on some last minute machining.

One of the minor quibbles over the Coronado external etalons is the open T-Max tuner design, which can allow contaminants through the gap when open:
TMax open.jpg
Addressing this in the SM90's, I used a "sprung" internal thin plastic ring to cover the gap and block this from happening - but lost about a mm or two of aperture. In the SM140, I instead decided to use some black elastic fabric material around the periphery, and secured it at both ends under the hinge plate. The OEM steel hinge plate bolts were corroded with rust, so these were replaced with stainless steel.
TMax gap covered.jpg
Hoping I will have some good weather with steady seeing in the next weeks as "first light" approaches.


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Re: Dream come true!

Post by Derek Klepp »

I look foward to your first light reports Bob.


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Re: Dream come true!

Post by Bob Yoesle »

I guess its time for an update to my saga - as you will see, things have not gone as expected...

After a great deal of effort, all the necessary parts were made or modified, and assembled. I took particular care to make sure optical and mechanical alignments were as best as I could accomplish.

Here focuser and objective alignments are optimized:
Focuser align IMGP3687.jpg
IMGP3716.JPG
The SM140 tilt-tuning rod is installed:
Tilt tuner rod.jpg
September 27, 2015 first light of the competed SM140/90 CR6 OTA:
IMGP3712.jpg


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Re: Dream come true!

Post by Bob Yoesle »

My first views were very disappointing -- off-band and considerably non-uniform. To get any detail I had to open the SM140 T-Max all the way.
R_180827.jpg
SM140/90 @ native CR6 EFL ~ 1200 mm.

The good news was the resolution appeared good given the low altitude and generally average to poor seeing conditions.

I decided to do my usual side-by-side comparison with with the "reference" DS SM90/90 system, and that's when the true magnitude of the off-band issue became evident.

Comparison configuration:
SM140 SM90 compare SM.jpg
Using a custom high-quality focal reducer to get similar EFL's, both the visual and imaging results leave little doubt as to the off-band issue:
SM90-90 vd SM140-90 Comapare SM.jpg
EFL's ~ 900 mm
Last edited by Bob Yoesle on Mon Nov 23, 2015 7:08 am, edited 1 time in total.


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Re: Dream come true!

Post by Bob Yoesle »

Over the next several weeks of despondency, I contacted Markus Ludes, who was at a loss to understand why I might be having such difficulties. He advised contacting Andy Lunt at Lunt Solar Systems, who I shared the above imagery with.

Andy asked me to call him, where he advised me that the oft-cited theory of double stacked etalons needing to be off-band to either side of the H-alpha line was completely erroneous. Andy stated that each etalon should be able to come exactly on-band in order to give best performance, and asked me to obtain images with each filter individually. For the front SM140, Andy asked me to obtain images with the filter tilt tuner closed (no tilt), mid-tilt, and maximum tilt. It took several weeks to get any clear weather, and when I did the seeing was very poor, but adequate to reveal the needed information:

No tilt:
Frnt no tilt.jpg
Frnt no tilt.jpg (118.4 KiB) Viewed 13474 times
Mid tilt:
Frnt mid tilt.jpg
Frnt mid tilt.jpg (117.1 KiB) Viewed 13474 times
Max tilt:
Frnt max tilt.jpg
Frnt max tilt.jpg (130.96 KiB) Viewed 13474 times
This behavior is quite different from every other front etalon I have used, where the optimum position is mid to near closed tilt to be on-band, and I have never observed a continuum image as seen in the SM140 with no tilt. This indicates the SM140 CWL is tuned quite high, and just begins to come into the red wing of H alpha with the maximum tilt available.
Last edited by Bob Yoesle on Mon Nov 23, 2015 7:10 am, edited 2 times in total.


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Re: Dream come true!

Post by Derek Klepp »

Thanks Bob does that mean you need a bit more tilt or that's it as far as being on band?


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Re: Dream come true!

Post by Bob Yoesle »

Next, for the internal SM90, Andy advised using the DERF ahead of the etalon to reduce incipient IR, as well as the RG630 ERF which is installed just ahead of the collimator lens:
IMG_20151004 SM.jpg
Andy requested that I try several different internal module placements to see if any change produced an improvement. No significant change was observed compared to the theoretical best placement based on the measured FL of the collimator lens:

Theoretical best placement:
777.jpg
777.jpg (136.18 KiB) Viewed 13473 times
Placed 90 mm farther away from the objective:
867.jpg
867.jpg (155.93 KiB) Viewed 13473 times
Placed 110 mm closer to the objective:
667.jpg
667.jpg (143.5 KiB) Viewed 13473 times
The changes in seeing affect the quality of the images, but the overall contrast and contrast uniformity remains essentially unchanged, with little change in the peripheral band-pass as well. This is a testament to the relatively large size of the internal etalon and the long focal length of the collimator lens, which results in minimal field angle magnifications.

But once again we can see this etalon too is not on-band, and therefore the combination of etalons could not be on-band either. My suspicion was that the internal SM90 filter might be a standard production SM90, which again would be tuned hi -- but under "normal" circumstances it would be "tiltable" to bring it on band. In the case of the internal module, no provision for tilt tuning was provided -- it remains completely fixed in the etalon cell and thus off-band Hi.
Last edited by Bob Yoesle on Mon Nov 23, 2015 7:13 am, edited 1 time in total.


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Re: Dream come true!

Post by Bob Yoesle »

I also had the opportunity to contact John Hunter of Light Machinery Etalons in Canada. John advised me to obtain a Hydrogen laboratory spectrum tube in order to perform an etalon fringe analysis. So I headed back to Yakima Valley Community College and my friend Dr. Rodrigue was happy to assist.

The etalon fringe test is what is used at Lunt as well for determining etalon quality and specs:
Test crp SM.jpg
Test crp SM.jpg (57.47 KiB) Viewed 13473 times
I felt I had a pretty good handle on how to perform this test. Note a diffuser screen is used to make the fringes a bit more visible. I brought the lab equipment home and made a similar simple test diffuser set up:
Test set-up.jpg
When viewing the etalon fringes, one sees concentric circles, and the spacing of the circles is the FSR -- free spectral range. The tightness or "crispness" of the fringe indicates the finesse - sharp fringes with no intervening light between the fringes indicate excellent finesse. If there is a central spot dead-center the etalon is on-band. If the central spot expands, or becomes a circle, the etalon is showing it is off band, and the larger the central circle the father off-band the etalon is.

So first up was a reference SM90 etalon. This is my primary DS etalon, tuned hi, but requiring the least amount of tilt to come on band at my elevation of 610 m:
SM90 Objective.jpg
SM90 Objective.jpg (157.45 KiB) Viewed 13473 times
Next up is the internal SM90 of the new telescope system:
SM90 Internal.jpg
SM90 Internal.jpg (111.73 KiB) Viewed 13473 times
And here's the SM140 external:
SM140 External.jpg
SM140 External.jpg (147.87 KiB) Viewed 13473 times
These results seemed to confirm my suspicions. The internal SM90 looks almost identical to my reference SM90 front etalon, tuned perhaps just a bit higher. The external SM140 has a much larger central spot-circle, indicating it is tuned to a much higher CWL. Mr. Hunter and associates indicated that the DS system would not come on-band unless used at about 2000 m or greater elevation.

So again, there's no way this system could perform anywhere near on-band at the altitudes I typically observe at -- 0 to 1200 m elevation. The good news is that both etalons appear to have absolutely superb finesse.
Last edited by Bob Yoesle on Mon Nov 23, 2015 7:17 am, edited 1 time in total.


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Re: Dream come true!

Post by Bob Yoesle »

So great, now what --
the scream.jpg
the scream.jpg (158.94 KiB) Viewed 13465 times
my dream turned to nightmare solar telescope is too heavy for a paperweight, and not heavy enough for a boat anchor.

Well the story is not over. On seeing these results, Andy has graciously agreed to evaluate the etalons and refurbish them to be able to perform as intended at the altitudes I will use them at. :hamster:


This will likely require re-tuning the SM140 CWL via new spacers. The internal etalon will need to be tuned as well, as pointed out on the Lunt web page http://luntsolarsystems.com/etalons-ext ... -internal/
The evolution of internal etalons has taken several steps. The original systems had internal fixed etalons that sat behind a re-collimating lens set (these lenses work to bring the light rays back to parallel). The light from the etalon was then re-focused back to the image plane. These systems cannot compensate for changes in altitude and air pressure. Taking this system from sea level to 8,000ft would not work...

The next step is the introduction of some tilt. This works similar to the tilt on the front of a system. However, due to both off axis light rays that could not be re-collimated with a simple lens, and the angles created by the Sun’s size, the etalon can only be tilted thru a fraction of a front mounted system... The removal of the tilting from the internal system is providing stunning results... This [Doppler True (pressure) tuning] technology has certainly improved the dedicated system...(Empahsis added)
Therefore I anticipate the internal etalon will require vacuum tuning, or need retuning of the CWL to allow for pressure tuning.

To be continued, and holding my breath to hear what lies ahead...
Last edited by Bob Yoesle on Mon Nov 23, 2015 7:20 am, edited 1 time in total.


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Re: Dream come true!

Post by marktownley »

It's a shame to hear the journey isn't as you would have liked Bob, but you have most certainly been thorough in your approach. The only thing I can think to suggest is for Lunt to change the etalon spacers?


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Re: Dream come true!

Post by marktownley »

Lol, you beat me to the post! :D That's good news!


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Re: Dream come true!

Post by Bob Yoesle »

Thanks Bob does that mean you need a bit more tilt or that's it as far as being on band?
Hi Derek

That's the limit for tilt, which is already too much as it introduces significant contrast non-uniformity of the off-band image. As the rest of the story indicates, the SM 140 CWL is too high for use at my altitude, and this will need to be addressed directly.

Thanks Mark, keeping my fingers (and toes) crossed ;-)


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Re: Dream come true!

Post by Valery »

Bob,

Why not ask Mr. John Hunter to determinate the necessary spacers thickness, to make them and to assemble the etaion
at the LM laboratory?


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Re: Dream come true!

Post by Montana »

Oh dear Bob, I hope they fix it soon and the dream will come true ;)

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Re: Dream come true!

Post by Solar-Cologne »

Hello Bob,

Your problem is very interesting.
I read all your posts here, but i never find the words:
the two etalons must be rotated against each other to find the best h-alpha :!:

Excuse me, if I have overlooked it.

but you had make two mistakes. I phoned with W.Lille and Oliver about your problem.
I ts a great mistake to use an ED or an APO-refraktor for watching h-alpha, especially a TAK with a fluorite lens.
An ed/apo is corrected for the green wavelength and there are allways speciall glasses in it, not good for h-alpha.
And a fluorite lens too, is not focus-stable in h-alpha, like a Zeiss-APQ :!: :!: :!:
I have made many experiments with ed, and see it often, when i may have a look through an apo-self-made h-alpha-scope.

Use a asphäric-chromatic single lens, like a W.Lille h-alpha-chromat-scope:

http://sonnenfernrohr.de/2015/03/lille- ... fertigung/

or use a Fraunhofer-refraktor, which is corrected at the red wavelenght.

Please do some experiments and share your results here in the forum.


Sorry, the SM140 is not the "Holy-Grail", because there are worldwide 4 pieces of a Lunt 160 frontetalon.... :beanie:

sunny Greetings :D
Achim
Last edited by Solar-Cologne on Mon Nov 23, 2015 5:02 pm, edited 2 times in total.


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Re: Dream come true!

Post by Bob Yoesle »

Hi Valery
Why not ask Mr. John Hunter to determinate the necessary spacers thickness, to make them and to assemble the etaion at the LM laboratory?


I did get a "ball-park" estimate from John:

Code: Select all

Typically we charge about US$20,000 for large aperture etalons, I expect the repair would be about half of that (and may not be successful).
Moreover, this estimate did not include the internal SM90, nor the need to adapt the internal module (or make a new one) to be vacuum/pressure tuned.

The SM140 has 12 spacers around the periphery in addition to the central spacer (the industry standard is three to six spacers on the periphery -- the SM90 has 9 + 1 central)... Bill Dean -- who worked at Coronado when the etlon was made -- told me that the SM140 etalon is one of the trickiest ever made, and the only people he would trust to pull off the repair would be Andy or Brian Stephens. I believe Andy (and/or Brian) have a sincere interest in the project as they were the OEM. Additionally, Andy has very generously stated he will only charge for materials; he is donating the labor to our Friends group for solar outreach. The new scope will therefore be generously adorned with Lunt Engineering decals following successful repair.
Oh dear Bob, I hope they fix it soon and the dream will come true ;)
Thanks Alexandra -- me too! And if not, I have vowed to give up solar astronomy and take up stamp collecting ;-)
the two etalons must be rotated against each other to find the best h-alpha :!: ...or a Fraunhofer-refraktor, which is corrected at the red wavelenght... Sorry, the SM140 is not the "Holy-Grail", because there are worldwide 4 pieces of a Lunt 160 frontetalon....
Hi Achim,

Clocking is not an issue and would not solve the root issue of the too hi a filter CWL.

I did indeed know about the problems with fluorite APO's from discussions with Mike Jones. That's why I specifically bought only the filters from Markus, and adapted them to the CR6, which is a well corrected fraunhofer achromatic refractor.

I didn't know about the 160's -- any details? But part of the "Holy Grail" status for me is the large internal etalon which allows for the most optimum field angles (contrast uniformity) for the double stacking. I doubt any 160's are double stacked with a 100 mm internal etalon, however ;-)

Thank you all for your interest and concern -- I will keep you posted.
2x04-tb_or_not_tb179.jpg
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Last edited by Bob Yoesle on Mon Nov 23, 2015 4:34 pm, edited 1 time in total.


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Re: Dream come true!

Post by Solar-Cologne »

Hi Bob,

thanks, i am allways interested in h-alpha and the problems that may arise.

About the SM160, Wolfgang Lille, knows Andy Lunt personally, and he tell me about this very rare front-etalons.
I never seen one of them.
With using google, i found this links:

http://luntsolarsystems.com/etalons-ext ... -internal/
http://www.khanscope.com/productdetails ... uctID=2020
https://www.google.de/search?q=lunt+160 ... I4ChCwBAgk

sunny greetings :D
Achim


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Re: Dream come true!

Post by Solar B »

Fingers / toes crossed here to Bob for a resolution of your fine SM140/90

I'd be surprised if there are any 160s around ? (would love to see one though)

Markus obviously uses a 230mm with rear mounted etalon (but doesn't everyone now) :)

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Re: Dream come true!

Post by Bob Yoesle »

Hi Achim and Brian,

I was aware of the reference to the LS160F from the time of the original "external-internal" blog post a few years ago, but didn't know any were actually made (and the front etalon pressure tuning likewise apparently was abandoned). I have never seen them mentioned or discussed since. Would be great to know where they ended up -- nothing shows up on my google search.

The images I see on the Kahn site for the 160 are actually the discontinued LS75F "root 3" etalon...


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Re: Dream come true!

Post by mdwmark »

Hi Bob,
Andy will fix you up. Its his system, he is the best person to deal with the problem.
Mark W.


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Re: Dream come true!

Post by Bob Yoesle »

Thank you Mark -- have a great Thanksgiving all!


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Re: Dream come true!

Post by Bob Yoesle »

Got an update on the etalon refurbishment, and things are progressing. Last week I asked Andy if he had a chance to evaluate them yet, and I received the following:
Hi Bob,

Yes we have.. : )

The front mounted etalon was completely reworked. We took the etalon apart and re-assembled using new spacers. The bad news is it took 10 attempts, the good news is that we were able to get the etalon to a uniform and excellent tune. Only a very slight tilt will be required.

The internal etalon is very close to be ideal being just slightly high.
To compensate for this we are going to re-house the etalon and change it's tuning point slight lower.

I imagine that this will be completed by end of next week.

I did test the IR ERF and found the surface to be very good.

Let me know if you have any questions.

Best Regards,

Andy Lunt
Hoping to have additional updates in the coming weeks. Again -- much appreciation to Andy for his efforts... Two thumbs up!


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Re: Dream come true!

Post by marktownley »

Really good news Bob, i'm excited for the project :)


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Re: Dream come true!

Post by Bob Yoesle »

Finally had a break from snow and rain this past weekend, which presented an opportunity to check things out through the "new" filters. Although seeing and transparency were very poor, temps rose to ~ 10 C, and I did manage to verify much better performance!

The front 140 etalon comes on band with minimal tilt, and by rotating ("clocking") the etalon cover with the Baader DERF160 I can shift the ERF reflection off-disc so that additional tilt is minimized. There is another out-of-focus internal reflection, which I think is caused by the SM90 RG630 ERF I added to the 90 mm internal etalon -- I may have to give it a bit more tilt after I upgrade it to a Lunt RG630 ERF 105 with IR blocking... or I may forego the internal ERF for a Baader H alpha RG substrate filter placed on my BF30 with the KG3 ITF replacement.

Both etalons are now essentially on-band, and the full disc uniformity is excellent!
Coronado140-90 preliminary results SM.jpg
Shown above: Milky skies hampered contrast, but the uniformity and CWLs are about right-on, with just a hint of a double-limb.

As noted by Andy above, the internal etalon remains fixed, and has had it's CWL blue-shifted slightly by mechanical pressure-tuning with the addition of a foam ring, which can be compressed by the collimator lens cell. The tuning can be adjusted using the hydorgen spectrum tube, and getting the inner ring down to being just barely a "donut," with only a hint of a central hole.
Internal pressure tuning SM.jpg
Looking forward to a better opportunity to check the system out when atmospherics are better. Ultimately I may consider a vacuum tuning system for the internal etalon, but this will require some additional thought, as the mechanical implementation will require a major engineering effort or new etalon housing and/or OTA. It may be unnecessary with additional fine-tuning and better seeing/transparency.

A special thank-you goes to Andy Lunt and Brian Stephens for their outstanding efforts to support, inform, and "make it right."
Last edited by Bob Yoesle on Wed Mar 02, 2016 1:22 am, edited 2 times in total.


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Re: Dream come true!

Post by Marcello »

Hi Bob,
congratulation for the happy of this long story, and to Mr. Andy for the excellent assistance!

The image looks great, I can only guess how wonderful is the view at the eyepiece!

cheers
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Re: Dream come true!

Post by Solar B »

Fantastic news Bob and it does appear to be onband in the image even giving
the poor seeing :cool:

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Re: Dream come true!

Post by marktownley »

Brilliant! Bring on spring!


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Re: Dream come true!

Post by Valery »

Congratulates, Bob!

Looking for your DS images full disk and high res.


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Re: Dream come true!

Post by Derek Klepp »

Good to hear Bob.


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Re: Dream come true!

Post by Bob Yoesle »

I have a bit of progress to report on this seemingly endless project - a lot of time and effort which is turning out to be worth it in the end.

Views through the scope in the early spring were good, but not quite what I had hoped for. While I had hoped the mechanical internal etalon tuning would work, it proved to be impractical - as once the setting was chosen, the telescope then became fixed with the internal etalon tuning, and would require complete disassembly to adjust further. Changing atmospheric pressure and temperature seemed to prevent optimum performance.

So I decided the only way to go would be pressure tuning. Once again I relied on the wonderful help of Dan Steinmetz and his students at Perry Technical Institute.

I didn't want to disassemble the etalon from its housing, and Dan advised there was plenty of clearance around the etalon to drill and tap an access for a vacuum fitting. A bit nerve racking waiting for the process, but all went well!
20160727_131959(0) SM.jpg
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20160727_132826 SM.jpg
20160727_132826 SM.jpg (153.61 KiB) Viewed 12922 times
Next was determining how to seal the etalon collimator module. I decided on a silicone gasket and vacuum grease approach. Here's my dining room table workbench. I purchased the gasket material, and Perry Tech cut custom gaskets for both the collimator and refocusing lens cells, and the cell mounts themselves.
IMGP3898 SM.jpg
IMGP3898 SM.jpg (284.13 KiB) Viewed 12922 times
Applying vacuum grease to the lens cell:
IMGP3900 SM.jpg
IMGP3900 SM.jpg (240.93 KiB) Viewed 12922 times
My look of disappointment when seeing the vacuum would not hold:
IMGP3905 SM.jpg
IMGP3905 SM.jpg (300.78 KiB) Viewed 12922 times
I tried redoing the seals several times, and in the end all I had were sore wrists from the multiple assembly and disassembly tries (silicone grease is thick - and quite messy) -- and no sealing. A quick call to Lunt, who advised sealing the lens itself with clear RTV silicone applied inside the cell, and applying the same to the outside of the lens cells to achieve the best seal possible. This did the trick:
IMGP3914 SM.jpg
IMGP3914 SM.jpg (207.16 KiB) Viewed 12922 times
Here's the completed internal module, with a Lunt IR blocking ERF ahead of the negative collimator lens, the vacuum fitting, and OTA positioning bolts:
IMGP3916 SM.jpg
IMGP3916 SM.jpg (253.38 KiB) Viewed 12922 times
Perry Tech cut longitudinal slots along the OTA which were necessary to allow adjustment/optimizing the position of the internal module, and passage of the vacuum fitting. Note the nice brass setting bolts on the curved aluminum pressure blocks (which I faced with felt to protect the OTA finish):
IMGP3917 SM.jpg
IMGP3917 SM.jpg (285.07 KiB) Viewed 12922 times
The completed OTA with a Ralston Instruments precision vacuum/pressure hand pump attached:
IMGP3921 SM.jpg
IMGP3921 SM.jpg (235.18 KiB) Viewed 12922 times
Here's the OTA in place, with the ball check valve and disconnect. The OTA is quite heavy at 40 pounds with both etalons:
IMGP3929 SM.jpg
IMGP3929 SM.jpg (215.55 KiB) Viewed 12922 times
A close up of the Ralston Instruments pump, showing the days optimum vacuum of -4.5 PSI. The level of pressure is roughly set by the hand pump on the right side, and the fine adjustment is accomplished by the threaded fine-tuning knob of the left side -- very fine adjustment is possible. I found this preferable to the pressure tuners I have used, due to the fact that the adjustment is accomplished off-scope and no movement of the image is involved during tuning.
IMGP3924 SM.jpg
IMGP3924 SM.jpg (237.25 KiB) Viewed 12922 times
Initial evaluation was performed yesterday just before the weather deteriorated here in the Pacific Northwest. Despite poor transparency, everything was perfectly on band! I first viewed the image single stack with the internal 90 mm etalon, and tuned it up perfectly. Adding the SM140 removed the double limb and showed much improved contrast. But boy is the seeing aperture-limiting. Therefore no imaging was attempted. Additional fine tuning of the collimator position, OTA finish details, and possible addition of a 105 mm B+W Kaesemann circular polarizer behind the ERF lie ahead - weather dependent and it might be spring until these issues can be optimized.

And being somewhat OCD, I'm looking to adapt a defunct Helios etalon assembly as an internal triple stacking module for use within the AP 2.7 inch focusers I use for my H alpha scopes:
IMGP3938 SM.jpg
IMGP3938 SM.jpg (157.18 KiB) Viewed 12922 times
Looking forward to some steady clear weather for my first real observation and imaging attempts. Might have to get down to California for the winter shake down.
IMGP3933 SM.jpg
IMGP3933 SM.jpg (284.95 KiB) Viewed 12919 times
IMGP3936 SM.jpg
IMGP3936 SM.jpg (307.84 KiB) Viewed 12918 times


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Re: Dream come true!

Post by christian viladrich »

What a beautiful and amazing work !
I am delighted you start having good results paying back your effort.

BTW, if I run the math, I find you will have a 0.67° sweet spot (in diameter) with the 140/90 etalons. This is if we allow a CWL shift of only 0.25 A at the edge of the sweet spot.


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Re: Dream come true!

Post by marktownley »

It's looking fantastic Bob!


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Re: Dream come true!

Post by Bob Yoesle »

Thanks Mark and Christian - and thanks Christian for the sweet spot calculation ;-)


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Re: Dream come true!

Post by george9 »

Amazing, Bob! Good luck on the tuning. George


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Re: Dream come true!

Post by MapleRidge »

The scope looks great Bob...eager to see how the refinements work out.

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Re: Dream come true!

Post by Montana »

Wow! I'm looking forward to the first image through it :hamster:

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Re: Dream come true!

Post by Solar B »

In Awe of your fastidious work as ever Robert :bow

Now that's one Bino view I'd like to take :cool:

Oh and triple stack ... that should cut down on leakage !!

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Re: Dream come true!

Post by Bob Yoesle »

Thanks everyone! I have learned to be patient with this endeavor. I've also heard from Bill Dean that there may be additional 140/90's in existence somewhere, and that indeed the Vatican's was one of the first 90/60 DS scopes.

As it turns out the Helios might be totally unsalvageable - not only won't it come on-band in it's current state - it's put together with some kind of Loctite material. I will have to apply a hack saw or C4 to it to get it apart.

In the meantime, I'm also going to play around with a 105 mm Schneider (B+W) Kasemann circular polarizer for both the new telescope and the DS 90's. My previous experience with a smaller Kasemann for the CaK module indicates these appear to have very good optical quality. The advertised specifications show high quality components for an off-the-shelf photography CP:

"The Kasemann circular polarizer filter is completely edge-sealed for maximum durability under extreme climatic conditions. Lesser non-sealed circular polarizer filters can suffer from foil separation at the filter edges when used in these conditions. Käsemann polarizing foils are neutral in color, have a higher efficiency than conventional polarizing foils, and are cemented between high-grade plano-parallel optical glass, using a special cementing technique that resists delamination in humid climates. The resulting sandwich is then precision-polished again to achieve highly accurate plano-parallel surfaces... They are well suited for applications that require the highest possible imaging quality, especially with high-speed telephoto lenses and apochromatic lenses. " [Schneider Optics]

We'll see if they live up to this level of quality for solar telescope use. Hoping the weather may soon cooperate.


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Re: Dream come true!

Post by marktownley »

Thanks Bob, very interesting about the CP filter, i've just been googling them.


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Re: Dream come true!

Post by Spectral Joe »

Bob

Before getting violent with the Helios (not that I have anything against C4 in the proper place, having used hundreds of pounds of it in a previous career) I can try getting the relevant parts out without damaging them. If you're heading down to California in the future it would be a good thing to attempt together. I'm also working on some new equipment for bandpass measurement that you might find interesting.

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Re: Dream come true!

Post by antonello »

Hello Bob

Also I have had a dream for a long time and I worked for achieve it. For this purpose I have built a slight Truss (see picture 1)
1.jpg
1.jpg (88.16 KiB) Viewed 12708 times

for a 150 mm H-alpha Istar lens. After, I have purchased a Lunt Etalon, the model for 60 mm Double stack, for to put it inside the telescope. For this purpose, I have designed and made a 65 mm lenses collimator with a negative lens and a positive lens, to be used as shown in the second image (all this is attached to the end of the truss ....).
2.jpg
2.jpg (91.44 KiB) Viewed 12708 times
The whole system works perfectly, but my real dream was to have an Etalon of type "pressure" from 60 mm, promised for years by Lunt, but never realized.
My dream was to make (easily) a sealed cylinder for my Etalon (the two lenses help much) and to get the same H-alpha tuning not by inclination, but through the reduction in pressure within the cylinder sealed Etalon.
I thought it was a difficult thing because I've never seen him do this ... but then I saw your solution and I think that my dream It could be achieved. I saw that you are using a Hand vacuum pump Ralston
This pump is very expensive ($ 400). Is it necessary to such a precise pump? Would not be enough a more simpler pump, by that very Lunt used in "Etalon pressure type" (type syringe) used not for pressure, but for to create a vacuum?
Last thing. You or anyone is reading, know a formula that allows to calculate the shift of the frequency as a function of pressure?

Many thanks

Antonello


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Re: Dream come true!

Post by christian viladrich »

Hello Antonello,
I was just wondering where did you find the 65 / 400 mm lenses ?
BTW, in your case the diameter of the sweet spot is 22 arcmin, if you accept a max 0.25 A CWL shift at the edge of the sweet spot.
I've got an EXCEL file from Gert Gottschalk which calculates the CWL as a function of pressure. If you don't find it on the web, you can drop me a message.


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Re: Dream come true!

Post by Bob Yoesle »

Hi Mark - the Kasemann should arrive today and I'm looking forward to seeing what it can do and how much the decrease in image brightness occurs... unfortunately it might be a week or more until some sun arrives :-(

Hi Joe - would love to visit you again sometime for some "demolition" :) - I'll PM you...

Hi Antonello - what a beautiful telescope implementation!
You or anyone is reading, know a formula that allows to calculate the shift of the frequency as a function of pressure?
I think you can get to it by the formula's on these pages - get the air pressure and resultant refractive index put into the etalon wavelength formula:

https://www.gribble.org/cycling/air_density.html

and

http://emtoolbox.nist.gov/Wavelength/Documentation.asp

This graphic shows the relationship between refractive index and pressure, temperature, and humidity:
Effects of temperature pressure and humidity on refractive index of air.jpg
Effects of temperature pressure and humidity on refractive index of air.jpg (91.9 KiB) Viewed 12677 times
Depending on how high the etalon is tuned, I don't think you'd need more than - 5 PSI or so of vacuum - right now I'm finding about - 2 PSI is ideal for my internal 90.

You could first try one of these type of Mityvac automotive vacuum hand pumps to see if it would work:
MV8000.jpg
MV8000.jpg (121.33 KiB) Viewed 12677 times


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Re: Dream come true!

Post by Solar B »

That's a wonderful assembly you've got going on there Antonello !!
Loving the adonized red features to :cool:

If I may I think etalons that exhibit good finesse do/would benefit from pressure tuning ... however a regular
or average etalon perhaps not so and tilting would suffice ... this just from my rudimentary understanding.

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Re: Dream come true!

Post by Bob Yoesle »

Update.

I had some good weather and decent seeing for a couple of hours this past weekend, and finally had the views I have hoped for.

First single stacked; the internal SM90 etalon is quite uniform and superb in contrast, and is only slightly off-band high. About - 2.0 PSI of vacuum was required to bring the filter on-band (maximum filament density), and the range of adjustment is quite generous: +/- 0.5 PSI or greater. The increased aperture is awesome in good seeing!

Next: double stacked with the SM140 was a delight, no double limb, and the full-disc contrast was quite good, though not quite up to the DS SM90's - apparently nothing can touch them - DS ghosting required more tilt than I preferred to remove the ghost completely from the FOV.

Next I added the Schneider B+W 105 mm Kasemann circular polarizer - and solar Nirvana has been achieved! Though the image is dimmer, using my BelOptik KG3 BF30 still provided good image brightness, I could see no degradation in image quality at the 90 x magnification I used, and I couldn't get the grin off my face with binoviewing :-)

Some final tweaks and refinements are underway, and when I have good seeing I'll grab some images to post for the community.


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Re: Dream come true!

Post by robert »

Amazing journey to this point. Thanks for sharing it.
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Re: Dream come true!

Post by george9 »

Great to hear, Bob. George


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Re: Dream come true!

Post by marktownley »

Fantastic news Bob!


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Re: Dream come true!

Post by antonello »

Hello Christian

I designed the collimator with OSLO and optimized with Zemax so that none of the surfaces of the lens was flat, then I built the lambda/10 lenses from an important national industry. The system is expensive, but it is perfect.

This is the spots diagram with a perfect 150 mm f:10 lens
1_150mm_f10_perfect_lens_with_satta_collimator .jpg
1_150mm_f10_perfect_lens_with_satta_collimator .jpg (41.32 KiB) Viewed 12495 times
and this is the spots diagram with a commercial achromatic (150 mm f: 10)
2_150mm_f10_achromatic_with_satta_collimator .jpg
2_150mm_f10_achromatic_with_satta_collimator .jpg (42.34 KiB) Viewed 12495 times
The project was created for commercial purposes, but the result is still good when using catalog lenses with a flat side, as in this drawing
img010.jpg
img010.jpg (14.37 KiB) Viewed 12495 times
In this case, the quality is however still inside the diffraction
3_1_150mm_f10_perfect_lens_with_plano_concave_plano_convex_collimator .jpg
3_1_150mm_f10_perfect_lens_with_plano_concave_plano_convex_collimator .jpg (43.72 KiB) Viewed 12495 times
4_150mm_f10_achromatic_with_plano_concave_plano_convex_collimator .jpg
4_150mm_f10_achromatic_with_plano_concave_plano_convex_collimator .jpg (44.32 KiB) Viewed 12495 times
The important thing is that the two lenses are placed exactly as in the drawing above

You are right about the sweet spot, but I have realized the 150 mm to see details of the sun. To see the full surface of the sun I use the same Etalon and the same collimator system in a 100 mm f:10 telescope (Tal 100).
Here it is
tal_100_modified.jpg
tal_100_modified.jpg (89.78 KiB) Viewed 12495 times
The block collimator with etalon is universal and fits on all telescopes F: 10 or more, just put the first lens to F- 400 mm from the lens obiectiv (the precise value is achieved with Oslo (or ZEMAX).

Hello Bob
Thank you for all your interesting graphics. Thanks also to the information on the necessary pressure. Less 0.2 Bar, are a very small value. much smaller than I thought. Thanks also to the photograph of the economical aspirator vacuum. I had already thought of use one such tool that is used to suck oil from the brakes of cars, but you must change the tool for fine adjustment of the pressure. Precisely for this reason now I'm following a new road, testing a simply small piston for vacuum with adjustment by screw self made. I will experience everything as soon as the sun comes out.
Many thanks


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