ETALONS & BFs

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ETALONS & BFs

Post by pedro » Wed Jan 31, 2018 2:07 pm

ETALONS & BFs

Etalons and BFs I use to image the Sun (H-alpha)

WEBLINK:
http://re.apaaweb.com/etalons.html

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ETALONS (H-ALPHA SOLAR OBSERVATION)

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CORONADO SM90 + BF15

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CORONADO SM90

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CORONADO SM90II

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CORONADO SM90II

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CORONADO SM90II + CORONADO SM40II

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2X CORONADO SM60

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CORONADO SM60 + BF30

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CORONADO SM60 + CORONADO SM40

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CORONADO SM60 + CORONADO SM40

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CORONADO SM40 + CORONADO SM40II

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CORONADO SM40 + CORONADO SM40II (double stack)

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CORONADO BF30

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CORONADO BF10 + CORONADO BF15

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CORONADO BF10 + CORONADO BF15

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Image
LUNT H-alpha B1200

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LUNT Ca-K B1200

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ERF BAADER (110mm)

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ERF BAADER (165mm)

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APERTURE REDUCERS (IRIS)
Last edited by pedro on Fri Feb 02, 2018 4:04 pm, edited 1 time in total.

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Re: ETALONS & BFs

Post by Ibbo » Wed Jan 31, 2018 2:09 pm

oh shiny kit oh my:hamster: :hamster:


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Re: ETALONS & BFs

Post by Bob Yoesle » Wed Jan 31, 2018 3:00 pm

Thanks for posting these Pedro!

Your picture of the SM90II has answered a question I have had about the SMII front etalon with RichView tuning -- does it have mechanical pressure applied to the central spacer (in addtiton to the peripheral spacers)? The internal etalon's have a bolt secured to the negative collimating lens to apply this pressure:
SM60II richview etalon.jpg
SM60II richview etalon.jpg (115.2 KiB) Viewed 1131 times
Your photo clearly shows that the front etalon has a pointed shaft affixed to the center of the ERF that applies mechanical pressure to the central spacer area:
Coronado SM90II.jpg
Coronado SM90II.jpg (691.4 KiB) Viewed 1131 times
Obviously then this etalon requires the use of the OEM ERF, as opposed to the earlier versions without RV tuning.

In contrast to the DS SM40's, and all else being equal (!) The ideal double stacking arrangement would therefore appear to be an earlier SM filter which is on-band with very little tilt, removing it's redundant ERF, and using the SMII RV etalon as the double stacking etalon, which can be RV tuned on-band once the etalon is tilted to remove the ghost retro-refelctions...

The only other issue would be does Coronado use an IR blocking coating on the ERF? If not, an IR blocking filter should be used internally ahead of the blocking filter to protect it (especially if it uses an ITF). A Baader DERF, or even better the BelOptik UV/IR on KG3 would be suitable:

https://beloptik.de/en/uv-ircut-on-kg3-filter/

Indeed, this filter can replace a failed ITF, as long as an RG630 element (i.e. the SMII etalon ERF) remains in the system. This will provide a significantly brighter DS image as well, which improves both visual use and imaging.
Last edited by Bob Yoesle on Wed Jan 31, 2018 3:28 pm, edited 6 times in total.
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Re: ETALONS & BFs

Post by Montana » Wed Jan 31, 2018 3:15 pm

Another complete collection, although you are missing a Solarscope :)

Alexandra

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Re: ETALONS & BFs

Post by pedro » Wed Jan 31, 2018 4:55 pm

Thanks Bob & Alexandra

I tested a Solarscope but It was not a keeper

Well observed Bob. My SM90II seems to be decontacted (low contrast images). I sent it to Beloptik to be repaired.

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Re: ETALONS & BFs

Post by Valery » Wed Jan 31, 2018 5:28 pm

Nice collection, Pedro!


Bob, with all respect, I absolutely disagree that Coronado apply the pressure at the etalon for a fine tuning.
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Re: ETALONS & BFs

Post by marktownley » Wed Jan 31, 2018 5:50 pm

Valery wrote:
Wed Jan 31, 2018 5:28 pm
Nice collection, Pedro!


Bob, with all respect, I absolutely disagree that Coronado apply the pressure at the etalon for a fine tuning.
Yes, nice etalons indeed Pedro.

C'mon then Valery, why don't you agree? What's your take on it?
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Re: ETALONS & BFs

Post by Merlin66 » Wed Jan 31, 2018 9:40 pm

I had the misfortune to test and inspect a SM90 II etalon assembly (It was eventually returned twice to Meade!!)
With the Rich View adjustment it definitely applies pressure to the etalon.
I was surprised to see that in order to accommodate the Rich View mechanism the etalon has NO effective side support!!
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Re: ETALONS & BFs

Post by Derek Klepp » Wed Jan 31, 2018 10:43 pm

Thanks Pedro some nice discussion stimulated here.

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Re: ETALONS & BFs

Post by Bob Yoesle » Thu Feb 01, 2018 4:05 am

While the PST's "RichView" tuning may indeed be only tilt tuning (I haven't used one in a very long time) -- and Meade may be using the term generically for marketing purposes -- true RichView tuning does appear to involve compression forces applied at the peripheral and central spacers. Moreover, I have it directly from both Brian Stephens (Tucson Coronado, Lunt) and Bill Dean (Tucson Coronado) -- and now Ken -- that RichView tuning is mechanical pressure. See the discussion starting here:

https://www.cloudynights.com/topic/5324 ... try7902161

It includes a link to the original Coronado patent for "a compressive force is applied to a conventional air-spaced etalon filter to fine tune the thickness of the spacers to a precise and uniform optical length" that the David and Andy Lunt, Sidorin, et.al. authored, which Meade acquired along with the central spacer patent. Hence the development by Lunt for air pressure tuning - which is probably superior to mechanical pressure in any event.
My SM90II seems to be decontacted (low contrast images). I sent it to Beloptik to be repaired.
Hi Pedro,

I once had a decontacted etlaon, and it too had low contrast -- as in NO Contrast (e.g. continuum)! And there was a very large number of these images cast off preferentially to the side. So indeed I hope you have a decontacting problem, and not some other more difficult to remedy issue with poor coatings, surfaces, parallelism, or the like...
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Re: ETALONS & BFs

Post by Valery » Thu Feb 01, 2018 7:35 am

Direct pressure to etalon plates tuning in Coronado etalons is symply a myph.

I have modelled numerous etalons with Etalon Design software and I know how much etalon performance suffer from a smallest tilt between the surfaces of the etalon plates, from a RMS changes of the surface quality. There is no precise mechanism for a correct distribution of the pressure between all the spacers, include central one. There are NO such termally stable, very flat, equal in thickness and still elastical spacers.
To changes the thickness of mica we need HUGE pressure to apply. The mica will simply cracks than change it's thickness. And, no such powerful mechanism in the etalons.
The Rich View mechanism is an analog of this mecjanism in the PST etalon. It just change the range where the T-max tuner can work.
This allows Meade to lower the standards in the etalon manufacture and sell them so much cheaper than this were when etalons were
made at higher precision.

Here is a scheme of the Coronado telescope with internal RV etalon. See also the film where you see how jentle the effort which allow to tune the
internal RV. This is a childrich effort! The stick for the tuning can be unscrewed and then screwed in another threaded hole for tuning range change.
This pretty much all.

https://www.youtube.com/watch?time_cont ... V8gf6-Kl6w
Attachments
Coronado-ST-90-800-SolarMax-II-BF15-(0-5A-Double-Stack.jpg
Coronado-ST-90-800-SolarMax-II-BF15-(0-5A-Double-Stack.jpg (67.1 KiB) Viewed 1056 times
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Re: ETALONS & BFs

Post by Merlin66 » Thu Feb 01, 2018 7:54 am

Valery,
I hear you.....
But why then does the Rich View pressure tuning appear to work for many users of the SM60II, SM90II
I can assure you when I pulled the SM90 apart for testing there was definitely a centre pressure rod between the outer ERF and the internal etalon plates....
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Re: ETALONS & BFs

Post by pedro » Thu Feb 01, 2018 10:40 am

Very interesting discussion. I hope I will get my SM90II repaired...

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Re: ETALONS & BFs

Post by Valery » Thu Feb 01, 2018 5:06 pm

Merlin66 wrote:
Thu Feb 01, 2018 7:54 am
Valery,
I hear you.....
But why then does the Rich View pressure tuning appear to work for many users of the SM60II, SM90II
I can assure you when I pulled the SM90 apart for testing there was definitely a centre pressure rod between the outer ERF and the internal etalon plates....
In fact, this rod does not transmit any pressure to the etalon plate.

1. If it transmits the pressure - the ERF optical figure will be very heavily distorted and image quality should noticeably suffer.
2. It can't uniformly distribute the pressure over the surface of the etalon front plate so, that no figure change will result and even more
important that the space between the etalon plates will remain structly uniform.

I saw the disassembled Coronado 60 scope with internal RV etalon. No pressure at the etalon when tuning. The tuning stick can be just
moved from one hole to enother to change the range of tuning. Nothing else. Exactly the same purpose as in the PST etalon.

This is a simple misconception that Coronado use the etalon space change for tuning by applying pressure at the etalon plates.

I can guess that the rod just tilts the etalon as a whole (without space and optical figure change). There should be elastic rubber or
something like this behind the etalon.

Valery
Last edited by Valery on Fri Feb 02, 2018 4:19 am, edited 1 time in total.
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Re: ETALONS & BFs

Post by Merlin66 » Thu Feb 01, 2018 8:41 pm

Valery,
There was evidence on the SM90 II internals that some pressure was being applied to the front etalon plate.
sm90 003.JPG
sm90 003.JPG (78.97 KiB) Viewed 1023 times
sm90 002.JPG
sm90 002.JPG (46.46 KiB) Viewed 1023 times
Also I've seen examples of failures due to the central pin pressure cracking the support disk.
Optimized-solarmax60mm.JPG
Optimized-solarmax60mm.JPG (251.78 KiB) Viewed 1023 times
Optimized-solarmax60.JPG
Optimized-solarmax60.JPG (268.09 KiB) Viewed 1023 times
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Re: ETALONS & BFs

Post by Valery » Fri Feb 02, 2018 4:31 am

Merlin66 wrote:
Thu Feb 01, 2018 8:41 pm
Valery,
There was evidence on the SM90 II internals that some pressure was being applied to the front etalon plate.
sm90 003.JPG
sm90 002.JPG

Also I've seen examples of failures due to the central pin pressure cracking the support disk.
Optimized-solarmax60mm.JPG
Optimized-solarmax60.JPG
On the picture 2 you can clearly see the orange elastic rubber which acts as returning force when the RV moves the rod back.
The front end of the rod consists a rubber - to prevent too hard pressure at the front of the etalon. Do you really think that
such a rod construction can play the role in the etalon space change (extremely unifomely!!!) ??? Also, we than need to agree
that the rubber at the front of the rod and the orange rubber are more hard than etalon spacers or at leat close. Do you think
that there is such a material which is so elastic and still can be precisely optically polished - good enough for etalon precision???

Total absurd!

This is only for etalon tilt. So, the RV etalons has two stage tilting. This allows to produce etalons which work in a wider range
of conditions (sea level - barometric pressure, temperature), just like a PST etalon.


Valery
Last edited by Valery on Fri Feb 02, 2018 4:52 am, edited 1 time in total.
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Re: ETALONS & BFs

Post by Bob Yoesle » Fri Feb 02, 2018 4:40 am

Valery, I didn't quite believe or understand the tuning via compression of the etalon spacers myself, so I understand your skepticism. It wasn't until dealing directly with the tuning of my internal SM90 via compression forces, and then reading the patent and seeing that this was done for the early "hi-resolution" Tucson Coronado internal double stacking "modules" that I could accept that his must be the case for "RichView" tuning. However, I also don't understand how this central pin could be used in any way to effect tilt of the etalon, which would also seem redundant with the much simpler TMax tilting unit provided.

Wow Ken, those images are very revealing! Jeez, a cracked collimator lens to boot - yikes! You'd think they would add some sort of stop to help prevent pressure overload. Now I really believe air pressure tuning seems a lot better way to go.

I does look like there is some sloppily applied and unevenly spaced silicone on the lower of the two etalon plates for lateral support, which does make some sense if you're going to apply a compressive force to the upper etalon plate via the pin/shaft attached to the ERF.
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Re: ETALONS & BFs

Post by Merlin66 » Fri Feb 02, 2018 4:42 am

I'm having some difficulty with your tilt concept...why a central pin? Why not an edge contact like the PST? The reaction "rubber" in the PST has a small raised section to allow the tilt, nothing like that on the RichView.
We'll probably never know, unless someone breaks ranks in Coronado/Meade and properly explains what they're up to.
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Re: ETALONS & BFs

Post by Valery » Fri Feb 02, 2018 4:58 am

Merlin66 wrote:
Fri Feb 02, 2018 4:42 am
I'm having some difficulty with your tilt concept...why a central pin? Why not an edge contact like the PST? The reaction "rubber" in the PST has a small raised section to allow the tilt, nothing like that on the RichView.
The mass of the 90mm etalon is much larger than of a tiny 30mm PST etalon and too small rised section will quickly loss it's elastic ability at the weight and pressure or it does not has enough returning force for such a massive etalon. Very easy.
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Re: ETALONS & BFs

Post by Valery » Fri Feb 02, 2018 4:59 am

Merlin66 wrote:
Fri Feb 02, 2018 4:42 am
I'm having some difficulty with your tilt concept...why a central pin? Why not an edge contact like the PST? The reaction "rubber" in the PST has a small raised section to allow the tilt, nothing like that on the RichView.
We'll probably never know, unless someone breaks ranks in Coronado/Meade and properly explains what they're up to.

Very easy to check what is going on. One need to make an off axis 2" - 1,25" adapter. Put a laser collimator in
it and then adjust the RV. I bet he will see that laser ray will moves forth and back - according to RV rotation direction.

Another method needs DS etalons. Adjust etalons so, that you will see the ghost reflection(s) between the two etalons. Rotate the RV and I bet you will see that the reflection will move.


Valery
Last edited by Valery on Fri Feb 02, 2018 5:10 am, edited 2 times in total.
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Re: ETALONS & BFs

Post by marktownley » Sun Feb 04, 2018 7:34 am

OK, i'll throw my two penneth in... This is just Townley theory, that's all...

With air spaced etalons the 2 inner faces (separated by spacers) are parallel, obviously, for the etalon to work. However the outer face of each of the 2 etalon plates is at a slight angle to make each etalon plate slightly wedge shaped, this is to stop reflections internally within each etalon plate. This then means the whole etalon is actually wedge shaped.

If then this sits on a soft rubber gasket, in the case of the PST, and you screw down a tuning ring onto the other face then as the force increases on the etalon it will tilt in this housing. Here is a rather crude explanation and animation I did of this a few years ago

ImagePST tuning fig1 by Mark Townley, on Flickr

ImagePST tuning fig2 by Mark Townley, on Flickr

ImagePST tuning fig3 by Mark Townley, on Flickr

ImagePST tuning fig4 by Mark Townley, on Flickr

Imageetalon-animation by Mark Townley, on Flickr

My guess with the 90mm etalon is that that central pin is acting as the 'fulcrum' for the tilt, so that it is even across what is a much larger surface area than the PST.
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Re: ETALONS & BFs

Post by Valery » Sun Feb 04, 2018 9:04 am

Mark

The only remark: when the PST etalon has it's gap horizontal, it's CWL is a bit towards red. So, with pushing the rotation ring, one can scan the spectrum from red wing to blue ring.

In the Coronado Solarmax II RV with internal RV etalon when the etalon space is horizontal the CWL is at a red wing.

Valery
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Re: ETALONS & BFs

Post by pedro » Sun Feb 04, 2018 11:35 am

Great Townley theory, you should know. You took several of these etalons apart

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