A surprise in the LUNT CaK wedge

swisswalter · Post by **swisswalter** » Tue Apr 02, 2013 4:16 am

Guys,
Question....
Have we found a "good" CaK solution which doesn't involve the use of filter elements from an existing Lunt/ Coronado CaK scope?
I'me thinking of the members who don't have either of these to mod.....

Hi Ken

yes that is the problem. We still use very expensive, good working stuff just to mod it. At least we now have a solution for apertures above 100 mm

swisswalter · Post by **swisswalter** » Tue Apr 02, 2013 4:34 am

Hi all

more information about the filter stack, a close up through the microscope

Hi Ken

isn't that a solid etalon ?

colinsk · Post by **colinsk** » Wed Apr 03, 2013 2:12 am

[quote]Hi all

more information about the filter stack, a close up through the microscope

Hi Ken

isn't that a solid etalon ?

I don't think so. A solid etalon would be coating-substrate-coating. There would be two rigid supports laminated to both sides that likely would be . Are you thinking the "seal" hides a piece of mica? I would expect that the seal hides a stack of dielectric layers.

Post by **Merlin66** » Wed Apr 03, 2013 2:59 am

Hmmmm
I tend to agree with Colin.
The seal protects the inner coatings similar to the Ha ITF.....

swisswalter · Post by **swisswalter** » Wed Apr 03, 2013 4:43 am

Hi Colin, Hi Ken

thank you very much for your judgement. The search goes on.

Post by **Merlin66** » Thu Apr 04, 2013 12:21 am

Hmmmm
Some sunshine today...
I'm still processing the results (with the lo-res spectro first..)
First the Omega F0394DF019 Ca filter....
TOOOOO large a bandwidth - centred on the 394nm but extends well beyond both the Ca lines...
Double stacked with Oliver's UV-IR/KG3 filter - no significant difference..at least it tells us that the UV cut-off is below the Ca lines!
Not looking good.

swisswalter · Post by **swisswalter** » Thu Apr 04, 2013 4:22 am

Hi Ken

thanks for the update. What a pity, we have to dig deeper and harder.

Post by **Merlin66** » Thu Apr 04, 2013 4:29 am

Latest:
The 390EFLP (UV cut filter) just arrived at lunchtime from Omega Bob...
I set it up with the 394....same results as Oliver's UV-IR...
It is suppressing the UV just on and above the CaH line (397nm)- but still passing reasonable amounts of light....
Hmm - not the Holy Grail, but possibly a 10nm bandpass on the CaK.
I'll try some imaging tomorrow if the weather holds up....

swisswalter · Post by **swisswalter** » Thu Apr 04, 2013 4:44 am

Hi Ken

thanks again for the update. Good luck for tomorrow

colinsk · Post by **colinsk** » Sat Apr 06, 2013 2:16 am

Why look for a filter if mica is available? I am seeing people spend more money on trial and error than a refrigerator based coating machine would cost. Cleave your own. Wide bandwidths are not that hard.

swisswalter · Post by **swisswalter** » Sat Apr 06, 2013 4:34 pm

Hi Colin

thank you very much. That is of great interest to me. I do have finest mica from africa. I do not know what blancs/flats I need nor how that refrigerator based coating machine works and where to get one. Is there something to read up for an amateur, hobby amateur or profi

I would like to jump into such an adventure. Mabe you are willing to help.

My mica has been collected at that site

colinsk · Post by **colinsk** » Sun Apr 07, 2013 4:30 am

Walter, every refrigerator has a compressor that can be converted to a very efficient vacuum pump. With a bell jar, a electric heated pot with 20 or so cc's in volume to cook off a coating, a vacuum source and an oscillating crystal for measuring coating thickness you can coat your own optics. This is an old school method but not to hard to sort out. 60 years ago it was the only method to coat etalons.

email me at colink at designerinlight dot com and we can sort out a workable method. I have just read the old papers and have not tried to make it work yet.

swisswalter · Post by **swisswalter** » Sun Apr 07, 2013 8:02 pm

Hi Colin

thank you very much for your input. That sounds great. I'll be reading your papers and I'll try to get all the stuff needed. An other summer with all the weekends scheduled ;-)

Post by **Merlin66** » Wed Apr 10, 2013 10:28 pm

OK
Certainly not the best images!
But under the terrible seeing conditions the best of a bad lot...
I used the Baader Herschel wedge on the TS102, DMK21 for a white light comparison - a little "over cooked" to show the surrounding plage....
The CaK "offering" was with the ND and Continuum filters removed from the wedge and replaced by the Omega 394DF019 and the UV-IR/KG3 combo.
MUCH shorter exposure times!!!
The plage and edges of the umbra are clearer (under these very poor seeing conditions!)but little sign of the Ca "froth"
Where to from here?

swisswalter · Post by **swisswalter** » Thu Apr 11, 2013 12:50 am

Hi Ken

still a good result and thank you for sharing. I guess the 394 is still not narrow enough. Did you have a chance to combine it with the K-line or 390 andover ?

Post by **Merlin66** » Thu Apr 11, 2013 12:53 am

Walter,
No, I don't have either of those filters....
Do you think such trials would be worth while?

swisswalter · Post by **swisswalter** » Thu Apr 11, 2013 1:06 am

Hi Ken

I know only that I have tested some 50 plus combos and the secret is in that little square of the LUNT wedge or the single piece in the CaK scope. Looking at the plot of the LUNT stack, I see only that the flanges are very, very steep so we have a nice narrow bandwith. I did not yet have a chance to look into a plot of a CaK filter. Mark T. said, it looks optically very much the same as the LUNT stack, but seems to be a single piece of glassware

Post by **marktownley** » Fri Apr 12, 2013 9:49 am

A slight development in terms of updates here. If we look at the plot Walter got for the Yellow lunt filter below

Well compare this to the technical information for a 'type 6' from Andover

http://www.andovercorp.com/Web_store/Ge ... type_6.php

Now I believe that the yellow filter that both Lunt and Coronado use is one of these 'spike' filters - it ticks all the boxes; it has very steep sides and does not include any out of band blocking. Crucially looking at the Andover link on the right hand side of the graph (1.2xCWL) for CaK this would indicate the blocking ceases somewhere around 470nm which is what we see on Walters graph with the Lunt, and what i've seen with a visual spectrometer with the coronado. It also accounts for the in the UV which Walter picks up, and also is confirmed with the coronado filter and the 387nm not working to give us CaK proper.

So, kind of a step in the right direction, I might be brave and ask Andover for a quote for a custom filter of this type, but have a feeling it will be in the thousands...

swisswalter · Post by **swisswalter** » Fri Apr 12, 2013 3:16 pm

Hi Mark

thank you very much for digging that out. That looks promissing. The Type 6 filter has a max of 15x FWHM, the type 5 only 10x FWHM . Maybe we have to look into both of them. Hope you get soon a decent offer.

Do we have a plot of your CaK PST piece ?

Post by **marktownley** » Sat Apr 13, 2013 7:33 am

Hi Walter,

No plot of my CaK filter - i'm just working out where else it passes light using Sherlock Holmes style deduction. I could bring it over for you to scan it but it would have to be in the last week of August; I would also bring Mrs Townley rather than a short bald man with me.

Mark

swisswalter · Post by **swisswalter** » Sat Apr 13, 2013 7:53 am

Hi Mark

thank you very much. We are looking forward to having you here in august, that will be fun. We plan again an international outreach

You could always send the filter via post. It would be returned in just a couple of days.

Post by **marktownley** » Sat Apr 13, 2013 10:03 am

We'll make august a date then

I'll get the filter in the post to you at some point this week, will be interesting to see how it compares with the lunt then...

swisswalter · Post by **swisswalter** » Sat Apr 13, 2013 3:34 pm

Hi Mark

thank you very much. How about scheduling the international outreach special on the weekend 3/4 august 2013 ? The sooner we can log it on , the more visitors we will have.

Post by **marktownley** » Sun Apr 14, 2013 4:34 pm

Hi Walter, the governing factor here is Mrs Townleys holidays - she has the last week of august booked off, so would have to be weekend of 24th / 25th august... I should ask her first really :whistle:

swisswalter · Post by **swisswalter** » Sun Apr 14, 2013 4:57 pm

Hi Mark

what would we be without our bosses ;-)

Perfect, we book the international solar CaK outreach weekend on saturday/sunday 24th/25th august 2013, starting at 09.30 local time ;-) . Place N 47°27'14" E 9°33'3"

Food and drinks free

swisswalter · Post by **swisswalter** » Mon Apr 22, 2013 7:48 pm

Hi CaK freaks

just arrived home and took a pair of 395 nm chinese filters out of my mail box. I have mounted them already and we expect sunshine on wendsday :woohoo:

Looking at a light bulb they show a nice violett, but I guess they are much to broad. We will see, hopefully soon.

swisswalter · Post by **swisswalter** » Thu May 02, 2013 10:08 am

Hi all

another hope is gone

the chineese 395/30 filters are too broad, also in the case of a stack

the plot overview

the plot close up

the real result on the sun

Post by **marktownley** » Thu May 02, 2013 1:01 pm

Thanks for trying Walter...

swisswalter · Post by **swisswalter** » Thu May 02, 2013 5:03 pm

Hi Mark

don't be disappointed. The search goes on. The show must go on ;-)

Valery · Post by **Valery** » Tue Feb 25, 2014 12:42 pm

swisswalter wrote: The search goes on. The show must go on ;-)

I read the thread with a greet interest. Thanks to all who have participated.

But the question what is the end of story?

swisswalter · Post by **swisswalter** » Tue Feb 25, 2014 6:58 pm

Hi Valery

now, the show goes on, we just look out for the acteurs ;-)

Post by **marktownley** » Tue Feb 25, 2014 8:49 pm

We need someone who can manufacture these CaK filters economically to the 2.2a bandpass - Aries?

Valery · Post by **Valery** » Tue Feb 25, 2014 10:07 pm

marktownley wrote:We need someone who can manufacture these CaK filters economically to the 2.2a bandpass - Aries?

No, not at this moment and nearest future.

But what with Andor 390 + 393( ? ) filters combo? As I saw the pictures, they are nearly as good as with Lunt wedge and brighter.

swisswalter · Post by **swisswalter** » Wed Feb 26, 2014 5:23 am

Hi Valery

thank you very much. Yes you are right, the combo 390+393 is much brighter than the Lunt piece but not narrow enough

sullij1 · Post by **sullij1** » Thu Feb 27, 2014 4:57 am

Colin has the best idea I seen for a while. Perhaps a mica inserted in between the 10nm filters will tell if it is a small etalon. Colin Will calcite work as good as mica? How much is a suitable piece of mica? Can we find a source?

sullij1 · Post by **sullij1** » Thu Feb 27, 2014 5:01 am

WHOOOA! Cheap man! Ordering some now!

https://www.google.com/shopping/product ... N4BEKYrMAY

swisswalter · Post by **swisswalter** » Thu Feb 27, 2014 5:32 am

Hi Joe

yes, Mica is indeed cheap. $$$'s are not the problem. Cleaving one single thin error free sheet out of it is one of the challanges.

Post by **marktownley** » Thu Feb 27, 2014 6:57 am

I personally don't think just inserting a piece of mica between 2 filters like this will work at all - too many variables: Firstly we don't know if stacking 2 filters like this is effective, secondly we don't know the exact gap needed between the 2 filters if it did work, and it would have to be an precise gap. Thirdly, like Walter says there is no effective way for us to effectively cleave one single error free sheet at the right thickness (which we don't know).

By all means try it Joe, but Walter did some considerable trialing with the mica and trying to make spacers to repair a Lunt 50 etalon, with no proper success, and this is with Walter having access to facilities in a professional chemistry lab...

sullij1 · Post by **sullij1** » Thu Feb 27, 2014 10:28 am

Mark - Just to be devils advocate, I am going to disagree as Colin has pointed us this direction and mark Wagner has mentioned it in the past. I PMd Mark W over at the CN thread to come over and give us some input on the idea. Perhaps on mica thickness, filter stack configuration, quality of cleave and expectations on cut. I hope he engages us. He seems to be the man with the most experience on the mica issue.

Mark W are you there?

Post by **marktownley** » Thu Feb 27, 2014 11:07 am

Devils advocate is good!

sullij1 · Post by **sullij1** » Thu Feb 27, 2014 4:46 pm

Just feel I gotta, Mini etalon is an intriuging idea and I am very curious to see what it will take to create such device. Provding it is doable. I know Mark has posted stack sequences before but I don't recall us focusing specificaly on a mica eatalon in our stacks. Could be a interesting discussion.

swisswalter · Post by **swisswalter** » Thu Feb 27, 2014 9:06 pm

Hi Joe

I like that thread and "devils advocat" is a great term. They use to be very, very insistent, which is not very easy to scope with all the time.

Joe are you thinking of spacing two filters with a mica sheet or are you thinking of attaching two reflecting filters with a mica piece (daystar type)

I'm happy to send you some MICA from Africa if the interest is great, at no cost

an example

: MICA-Lump.JPG (487.76 KiB) Viewed 4055 times

sullij1 · Post by **sullij1** » Fri Feb 28, 2014 3:45 am

Hallo Walter, sorry for not getting back sooner - been a busy day. The question you ask is a good one. I am interested to see what Mark Wagner says. I have thought about both methods but not yet decided. You mentioned "attaching", attaching perhaps the way Lunt seems to have done? Yes. something similar. I have yet to go back and look at some of the information Mark W gave us earlier about how he constructed some of his etalons and filter stacks.

I remember in one thread we were engaged with Catlin on constructing the double pass filter that required a binding of two prisms with an optical contact agent that had a nome like Canada balm or something termed similar to this. Can you remember the name? I was wondering if that is what we are seeing on your micro side view of the Lunt. I am Wondering if that is a method? Or is mica spaced or optically contacted some other way?

Can two reflecting cavity type filters be bound either side of mica and achieve the band cut based on bifrigence alone or will there have to be BG or other type of glass spacing? Will there have to be a gap? or will the natural bifringence do the job if simply contacted or pressed to the mica mechanically?.

Or will there have to be reflective a cavity filter, a spacer, mica and then some type of blocker like a 390 series , 410 or other behind the mica? I reallly have to go back and read Marks previous posts. When my hard drive crashed i lost the links to those posts and the favorites I had saved in the old form did not follow me here. Thus I must dig through the old posts to find some of Marks Ws stack configurations. Do you have the links to those posts saved? If so can you relink me? Regardless, as I remember it we still did no speak specifically to optically binding mica, only polished crystal or glass etalons. So as you can see I have many questions on how exactly to approach the stack.

Best Regards,

Devils Advocate :seesaw

sullij1 · Post by **sullij1** » Fri Feb 28, 2014 3:47 am

Also, thank you for your wonderful offer to share your mica stash but I already have several packages being shipped as we write.

Peter Williams · Post by **Peter Williams** » Fri Feb 28, 2014 4:28 am

Canada Balsam is used as a cement when mounting microscope slides and cover glasses.
http://en.wikipedia.org/wiki/Canada_balsam
Also has good optical properties and used to cement lens elements together. Sounds like what you are referring to.

sullij1 · Post by **sullij1** » Fri Feb 28, 2014 4:41 am

Thank you Peter. Welcome to the nerdy conversations!

sullij1 · Post by **sullij1** » Fri Feb 28, 2014 4:59 am

Ah Ha, I found the old conversation but it only brings up more questions. i wonder if Mark W will share some new speculations after seeing the microscope view of the lunt magic back filter?

Here are the important parts of his previous post regarding etalon and stacking designs. But this makes me want to ask :

What was used as the "ITF" in this design?

What was the whole title of the "10 angstrom blocker" filter? that is "way" tight (narrow)! Where did they come from (source)? Did he mean 10nm CaK line type?

Or what was the bandpass on the 10 angstrom if the FWHM was 10angstrom?

Was this stack optically bonded as etalons are by letting the vacuum naturally form?

How is this accomplished with mica?

He stated "UV Polaroid when "thickness of the mica was not a ½ wave plate". What does this mean thickness is 1/2 wave plate mean? I thought wave value was measured on the flat surface not the thickness.

How is it measured?

MOSTLY - Not so much interested in the etalon design I think the "Paragraph 6 design" is very close to where we want to be.

FROM HIS PREVIOUS POST:

6) The difference in design of the two. The Daystar has two different K-line housing. The standard tiltable K-line is nothing more than two 10Ang blockers and an ITF. So it went AR, 10ang, BG25, ITF, 10ang, BG25, AR. Del would call this a 5ang filter but it was really not. But it does work, the plage was there and you could see prominence sometimes.
The etalon based filter was the other design. At K-line it takes much more temperature to move the bandpass. So unlike Ha the temperature control is less critical. The other advantage is the bandpass are broader so tilting can be use easier. I did put some etalon filters in the tiltable housing but added a strip heater and temperature controller to have more control of the bandpass.

Ok, the design for the etalon based filter would be AR, 10ang,(sometime BG25 and UV Polaroid )etalon, ITF, BG25,AR. You would need to use the UV Polaroid when the thickness of the mica was not a ½ wave plate or the next peak was not outside the blocker. This is because the mica is birefringent and will have two peaks. One for the different indexes on the different axis.
It should be noted that the UV Polaroid material we used is no longer made. So the ones I make need to be ½ wave plates to keep the HW as narrow as possible.

HEEELP!

sullij1 · Post by **sullij1** » Fri Feb 28, 2014 5:21 am

And one last question: If we are introducing a bifringment (mica) are we back to a tilting mechanism to hit - widen and narrow the passband?

Nite Nite!

swisswalter · Post by **swisswalter** » Fri Feb 28, 2014 5:33 am

Hi Joe

thank you very much for all the questions, I'm not in a position to answer them. But maybe we can discuss one thing after the other.

As I understood the 1/2 wafe plate means if you want to make a solid CaK filter stack the mica has to have a thickness of ~200 nm. In the case of a Ha solid etalon ~330 nm. I'm sure the mica is optically bound to the glass plates and there is no glue what so ever. The edges of the stack might be coated in order die protect the coatings of the glass plates from humidity and corrosion of the silver coating. personally I do not see me in a position to handle a 200 nm thin plate, you know how thin that is, just a fifth of a micron

sullij1 · Post by **sullij1** » Fri Feb 28, 2014 6:22 pm

Interesting Walter. Now I really want to see Mark Ws input on that.