Dream come true!

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Re: Dream come true!

Post by astroshot »

Very interesting read Bob. Well done! You must be chuffed!


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Re: Dream come true!

Post by Marcello »

Hi Bob, congratulations, a great and unique set up!

I didn't know about the Vatican observatory, I have to consider a pilgrimage!


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Re: Dream come true!

Post by Solar B »

Aye :)
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Re: Dream come true!

Post by Bob Yoesle »

Hi everyone, and thanks for the great comments and encouragement!

Brian -- where did you find that image of the HOTS 2005 conference which introduced the SM140? I think I recognize that guy in the background looking through the side x side twin refractors with the HW and DS SM90's ;-)
HOTS 2005 w arrow.jpg
HOTS 2005 w arrow.jpg (267.62 KiB) Viewed 13812 times
Marcello - I wouldn't make that pilgrimage just yet. I contacted the Vatican in order to obtain additional information on their 'scopes implementation, and they deny having such a telescope! The only scope they are aware of is this SM90 DS dedicated scope from the period:
Vatican Observatory Coronado.jpg
You might have to seek out the Swiss Guard or Opus Dei to see what happened to it!
Swiss-Guards.jpg
Swiss-Guards.jpg (95.7 KiB) Viewed 13812 times
So as it may turn out, I might have the only such filter system now in existence...

Work is progressing slowly on the SM140 telescope; still waiting on a set of new spacer rings for the SM90 internal module -- a local school for machinists has graciously volunteered to make them, but they are on summer vacation. I'm also looking into the optical theory for how to determine the exact focal length of the negative collimator lens, as this spacing is critical to optimum contrast performance, and no records apparently exist from the original scope design for specifying its focal length -- but the procedure looks pretty straightforward.

Another issue has cropped up -- upon close inspection the SM140's RG630 ERF is covered with fine sleeks, and has a significantly abraded area:
IMGP3629 sm.jpg
IMGP3629 sm.jpg (506.1 KiB) Viewed 13812 times
IMGP3629 crop sm.jpg
IMGP3629 crop sm.jpg (589.04 KiB) Viewed 13812 times
While these might not significantly harm the images, I just can't see having these defects with such a unique and valuable filter system, so I'm considering various options. Re-polishing is an option, but I also would want to re-coat the ERF with an IR blocking coating (blocking filter conservation, etalon stability), and so far I've only been able to obtain two quotes from firms willing to do a one-off IR hot mirror coating job, and it's $2500 - $3000 minimum! So I'm also considering a Baader DERF 160 which will fit within the existing tilted ERF cell, and using my spare RG630 ERF from my second SM90 to mount within the internal SM90 module in its original tilted cell - this should be a viable solution, and perhaps improve on the original as far as thermal protection and stability is concerned.

The OTA itself has been completed, and I have implemented a second-hand Astro-Physics 2.7 focuser, which was machined and adapted to the OEM focuser back plate:
New CR6 focuser.jpg
New CR6 focuser.jpg (209.82 KiB) Viewed 13812 times
In order to accommodate the longer focuser and use the BF30 and a binoviewer, the OTA was shortened about 50 mm, and I had an auto-body shop paint it white to give it that classy refractor look:
New CR6 OTA.jpg
I'll post again when significant additional progress is made.

B-)


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Re: Dream come true!

Post by marktownley »

sexy time! :D


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Re: Dream come true!

Post by Bob Yoesle »

I guess they should be sexy since we use them to look at "heavenly bodies." ;)

BTW - found out the real scoop -- The SM140 Markus thought went to the Vatican actually was a 140 with an internal 60 DS module (as used with the 90) that went to Mexico. The Vatican did get a single stack SM140 on loan, but it was returned. So I guess there was only one 140/90 filter set ever made...


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Re: Dream come true!

Post by arnedanielsen »

Wow! Big congratulations Bob! I'm looking forward to reading more about this project and of course see the resulting pictures!!

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Re: Dream come true!

Post by Montana »

Wow!! have you asked Ken at Solarscope whether he would do it for you? I know you are best friends :)

Alexandra


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Re: Dream come true!

Post by Solar B »

Hi Bob

I remember seeing the pic on "Coronado Solar Chat" at the time .... as to the identity of the gentleman with the dual 90s/wedge set up who knows ?? :)

Im sure I speak for all in wishing you the very best with your 140s development.
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Re: Dream come true!

Post by Derek Klepp »

Thanks for the update


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Re: Dream come true!

Post by marktownley »

Montana wrote:Wow!! have you asked Ken at Solarscope whether he would do it for you? I know you are best friends :)

Alexandra
:D


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Re: Dream come true!

Post by Bob Yoesle »

Thanks Guys!

Re: Ken @ SolarScope: I have nothing but the utmost respect for Ken and that he is a true perfectionist in trying to meet the needs of a very small niche market, and carve out a special area for such products in a small business environment. For example Ken was more responsive than I found Meade Coronado in answering email inquiries. Therefore I am grateful I had a chance to deal with him directly and honestly regarding my findings, and found him nothing but professional. Hopefully others will benefit from my difficulties, but moreover Ken's willingness to do all he reasonably could to address and correct most all of them.

BTW - As I mentioned previously Greg Piepol ( http://sungazer.net/ ) was also at HOTS 2005, made this whimsical image following our visit.
SM140 Piepol stack.jpg
SM140 Piepol stack.jpg (57.25 KiB) Viewed 13699 times
He, Paul Hyndman ( http://www.astro-nut.com/ ) and I (e.g: guess who ?!) all had/have Coronado DS 90's from that era, and had a great time under the sun down in Tucson that year... And we were all pretty amazed by the SM140/90 views -- just hoping I can duplicate what I remember...

B-)


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Re: Dream come true!

Post by Solar B »

Here's a pic from HOTS 2005 ... I recognise Gary & Greg .... I wish it was 05 again to (my first PST) .... ;-) .... Brian
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Re: Dream come true!

Post by Bob Yoesle »

Hi Brian - yep I recognize most of these guys; left to right - Bill Dean from Coronado, and solar imaging pioneers Gary Palmer ( http://www.solarminimum.com/ ), Greg Piepol, and Paul Hyndman... Indeed good times.
Last edited by Bob Yoesle on Sun Sep 13, 2015 11:39 pm, edited 1 time in total.


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Re: Dream come true!

Post by solarchat »

yep, I recognize those guys...


Piepol Palmer Ramsden.jpg
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Re: Dream come true!

Post by Bob Yoesle »

Some cool dudes there!

DEFR 160 arrives this week. Damaged ERF removed, getting prepped for ERF cell removal -- it's threaded pretty tight and it looks like some heat may be needed. The etalon cell and gold cover are much thicker than the SM90:
IMGP3632 sm.jpg


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Re: Dream come true!

Post by Solar B »

Let us not forget that its Mr Palmers image that adorns the PST box :)

Hi Bob ... Is the SM/ERF then encased in a small cell that we cant see and will
the 160 DERF fit perfectly in place of the existing ?

Brian
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Re: Dream come true!

Post by Bob Yoesle »

Here you go Brian -- a bit more progress as the DERF 160 arrived courtesy of Bob Luffel at Alpine Astronomical (great guy and service), and per the usual Baader fashion well packaged and in impeccable condition. The DERF 160 is larger in diameter than the OEM ERF by 15 mm -- but I determined it would fit directly in the OEM ERF cell if I used the retaining ring area for the DERF, and I would have a millimeter or two to spare all around. Thus I would not have to worry about turning down a delicate optic, releasing internal stresses, other unforeseen hazards, etc. It would be just a matter of using a different retaining method...

The first problem was removing the OEM ERF cell from the etalon cover, which required a special tool with the seating pins to fit the holes in the ERF cell... Once removed, three small holes were drilled and tapped around the periphery for the retaining bolts which would hold the DERF 160 in the larger circumference which held the OEM ERF retaining ring:
ERF cell mod.jpg
Note I used small pieces of black tape to ensure no direct metal to glass contact.

Below the DERF 160 is installed in the OEM ERF cell. It is shown from the eyepiece side in the cell sitting on the tape as noted above, and was centered using thin cardboard shims. Black silicone adhesive was used in multiple applications around the periphery to hold the DERF laterally, as is done with the etalon plates themselves. Finally, trimmed rubber washers secured through the retaining bolts act as restraining "clips" to prevent the DERF from ever falling onto the etalon plates themselves. One of the bolt/washers (shown at top) required a second partial washer to take up the space created by the tilt of the DERF in the OEM ERF cell:
DERF & cell mod.jpg
The OEM cell with the new DERF 160 fitted within the etalon cover:
DERF w cell-cover.jpg
The "acid test" would be if everything still worked when the cover was installed (e.g. the restraining bolts did not prevent full seating of the cover) - no issues there, and the DERF 160 looks as good (or better ;-) than the OEM, and retains the tilt of the original ERF:
DERF 160 installed.jpg
I'm very happy with this mod, as the DERF 160 should prevent any significant thermal issues affecting the front etalon itself (possible to some degree with such a large etalon in spite of the central spacer) and yield much better overall thermal stability. Additionally, it should protect the subsequent internal etalon and blocking filters from experiencing significant thermal loading an cycling. Moreover, it is used only for 88% of it's diameter which should avoid any possible edge issues, and Brian Stephens (Coronado Tucson / Lunt) told me that due to the large size, the BK7 substrate used for the DERF would have significantly less striae and better homogeneity than the RG630 ERF originally used. And obviously I have none of the OEM ERF sleaks and abrasions to deal with.

This week the machining students should have the internal SM90 RG630 ERF retaining ring and internal etalon centering rings completed, and further progress can be made ;-)


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Re: Dream come true!

Post by Solar B »

I'm loving it , loving it , loving it :)

Yes I do really like it !

Brian


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Re: Dream come true!

Post by marktownley »

I look forward to these updates Bob!


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Re: Dream come true!

Post by Bob Yoesle »

Getting much closer to first light! Yesterday was a busy day...

One of the main issues is how to determine as accurately as possible the focal length of the negative collimation lens, as it typically can not form a real image. However, there are methods. One, which is pretty straightforward, is a measurement of where the image of the sun (e.g. at infinity) produces a circular image exactly twice as large as the clear aperture:
negative lens FL simple method jpeg.jpg
negative lens FL simple method jpeg.jpg (15.61 KiB) Viewed 13448 times
This, however, might be subject to various inaccuracies, so I decided to go a more traditional route of optical bench testing, as described here: http://stao.ca/VLresources/sci-tie-data ... nt(060.pdf

All I needed was to find an optical bench. Luckily most college physics courses do an optics lab and have such equipment. I made contact with Yakima Valley Community College, and Dr. Stephen Rodrigue was quite enthusiastic about the project. I knew the objective/collimtor focal length(s) would be roughly the same ratio as the etalon diameters. Therefore a "ball park" focal length of 90/140 x the objective FL would be a close approximation: ~ 90/140 x 1200 = 771 mm.

We made multiple measurements at several lens spacing's in order to get a reliable and statistically valid sample. Dr. Rodrigue had an even more rigorous data reduction methodology than the referenced paper in the link above, and applied a inverted parameter of the scatter plot to derive a best fit line, with a 99% fit accuracy:
Dr Stephen Rodrigue YVCC.jpg
Here Dr. Rodrigue is working on the data reduction, with the optical bench in the foreground. The data indicate a focal length of - 77.7 cm:
Neg lens data.jpg
Neg lens data.jpg (160.36 KiB) Viewed 13448 times
I really enjoyed my time with Dr. Rodrigue, and he gets one of the first looks through the new instrument ;-)

The students working under the direction of Dan Steinmetz at Perry Technical Institute ( https://perrytech.edu/programs.html?programid=9 ) got back from summer vacation, and the internal etalon centering rings and the internal SM90 ERF retaining ring were completed this week. They also get a "first look." Here the rings are shown in preparation for painting:
New internal rings & SM90ERF retainer.jpg
So now just about everything is ready. Here is a photo of all the components worked on so far and/or ready for assembly:
Parts - final.jpg
Going left to right, top row: AP2.7 focuser machined and adapted to CR6 focuser end plate, shortened and painted CR6 OTA.
Second row: SM140 front etalon, DERF 160 in OEM ERF cell, etalon cover (now painted flat black on interior), SM140 T-Max tilt-tuner
Third row: forward internal etalon centering ring, negative collimator lens in cell, SM90 internal etalon in housing, refocusing lens in cell, rear internal etalon module centering ring, SM140 etalon cover
Bottom row: SM90 RG630 internal ERF in OEM tilt-cell, internal ERF cell retaining ring, original SM140 product warranty - dated May 11, 2005.

So it won't be long now - I have to make the internal etalon fixation rings or device - likely will adapt the OTA's OEM internal baffles, and finalize the mechanics of the front etalon adjustment rod.

To be continued...
Last edited by Bob Yoesle on Sun Sep 13, 2015 3:08 pm, edited 2 times in total.


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Re: Dream come true!

Post by marktownley »

You're having a lot of fun with this Bob :)


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Re: Dream come true!

Post by Carbon60 »

Immaculately engineered, Bob. We're all on tenterhooks waiting for first light.

I hope the viewing conditions do it justice!

Good luck.

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Re: Dream come true!

Post by astroshot »

Great to see your progress Bob.
Thanks for posting the updates.


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Re: Dream come true!

Post by MapleRidge »

An amazing project Bob...can't wait to see the first images form this assembly.

Brian


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Re: Dream come true!

Post by Solar B »

All good :)

Brian


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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 13462 times
Mid tilt:
Frnt mid tilt.jpg
Frnt mid tilt.jpg (117.1 KiB) Viewed 13462 times
Max tilt:
Frnt max tilt.jpg
Frnt max tilt.jpg (130.96 KiB) Viewed 13462 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 13461 times
Placed 90 mm farther away from the objective:
867.jpg
867.jpg (155.93 KiB) Viewed 13461 times
Placed 110 mm closer to the objective:
667.jpg
667.jpg (143.5 KiB) Viewed 13461 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 13461 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 13461 times
Next up is the internal SM90 of the new telescope system:
SM90 Internal.jpg
SM90 Internal.jpg (111.73 KiB) Viewed 13461 times
And here's the SM140 external:
SM140 External.jpg
SM140 External.jpg (147.87 KiB) Viewed 13461 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
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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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