A surprise in the LUNT CaK wedge

[swisswalter]

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]

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

[marktownley]

Thanks for trying Walter...

[swisswalter]

Hi Mark

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

[Valery]

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]

Hi Valery


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

[marktownley]

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

[Valery]

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]

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]

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]

WHOOOA! Cheap man! Ordering some now!

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

[swisswalter]

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.

[marktownley]

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]

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?

[marktownley]

Devils advocate is good!

[sullij1]

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]

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 2840 times

[sullij1]

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

[sullij1]

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]

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]

Thank you Peter. Welcome to the nerdy conversations!

[sullij1]

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]

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]

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]

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